Audio encoder, audio decoder, method for encoding an audio signal and method for decoding an encoded audio signal

ABSTRACT

An encoder for encoding an audio signal is configured to encode the audio signal in a transform domain or filter-bank domain, is configured to determine spectral coefficients of the audio signal for a current frame and at least one previous frame, and is configured to selectively apply predictive encoding to a plurality of individual spectral coefficients or groups of spectral coefficients which are separated by at least one spectral coefficient.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending InternationalApplication No. PCT/EP2016/054831, filed Mar. 7, 2016, which isincorporated herein by reference in its entirety, and additionallyclaims priority from European Application No. EP 15158253.3, filed Mar.9, 2015, and WO Application No. PCT/EP2015/063658, filed Jun. 17, 2015,all of which are incorporated herein by reference in their entirety.

Embodiments relate to audio coding, in particular, to a method andapparatus for encoding an audio signal using predictive encoding and toa method and apparatus for decoding an encoded audio signal usingpredictive decoding. Advantageous embodiments relate to methods andapparatuses for pitch-adaptive spectral prediction. Further advantageousembodiments relate to perceptual coding of tonal audio signals by meansof transform coding with spectral-domain inter-frame prediction tools.

BACKGROUND OF THE INVENTION

To improve the quality of coded tonal signals especially at lowbit-rates, modern audio transform coders employ very long transformsand/or long-term prediction or pre-/post-filtering. A long transform,however, implies a long algorithmic delay, which is undesirable forlow-delay communication scenarios. Hence, predictors with very low delaybased on the instantaneous fundamental pitch have gained popularityrecently. The IETF (Internet Engineering Task Force) Opus codec utilizespitch-adaptive pre- and postfiltering in its frequency-domain CELT(Constrained-Energy Lapped Transform) coding path [J. M. Valin, K. Vos,and T. Terriberry, “Definition of the Opus audio codec,” 2012, IETF RFC6716. http://tools.ietf.org/html/rfc67161.], and the 3GPP (3rdGeneration Partnership Project) EVS (Enhanced Voice Services) codecprovides a long-term harmonic post-filter for perceptual improvement oftransform-decoded signals [3GPP TS 26.443, “Codec for Enhanced VoiceServices (EVS),” Release 12, December 2014.]. Both of these approachesoperate in the time domain on the fully decoded signal waveform, makingit difficult and/or computationally expensive to apply themfrequency-selectively (both schemes only offer a simple low-pass filterfor some frequency selectivity). A welcome alternative to time-domainlong-term prediction (LTP) or pre-/post-filtering (PPF) is thus providedby frequency-domain prediction (FDP) like it is supported in MPEG-2 AAC[ISO/IEC 13818-7, “Information technology—Part 7: Advanced Audio Coding(AAC),” 2006.]. This method, although facilitating frequencyselectivity, has its own disadvantages, as described hereafter.

The FDP method introduced above has two drawbacks over the other tools.First, the FDP method involves high computational complexity. In detail,linear predictive coding of at least order two (i.e. from the last twoframe's channel transform bins) is applied onto hundreds of spectralbins for each frame and channel in the worst case of prediction in allscale factor bands [ISO/IEC 13818-7, “Information technology—Part 7:Advanced Audio Coding (AAC),” 2006.]. Second, the FDP method comprises alimited overall prediction gain. More precisely, the efficiency of theprediction is limited because noisy components between predictableharmonic, tonal spectral parts are subjected to the prediction as well,introducing errors as these noisy parts are typically not predictable.

The high complexity is due to the backward adaptivity of the predictors.This means that the prediction coefficients for each bin have to becalculated based on previously transmitted bins. Therefore, numericalinaccuracies between encoder and decoder can lead to reconstructionerrors due to diverging prediction coefficients. To overcome thisproblem, bit exact identical adaptation has to be guaranteed.Furthermore, even if groups of predictors are disabled in certainframes, the adaptation has to be performed in order to keep theprediction coefficients up to date.

SUMMARY

An embodiment may have an encoder for encoding an audio signal, whereinthe encoder is configured to encode the audio signal in a transformdomain or filter-bank domain, wherein the encoder is configured todetermine spectral coefficients of the audio signal for a current frameand at least one previous frame, wherein the encoder is configured toselectively apply predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theencoder is configured to determine a spacing value, wherein the encoderis configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value;

-   -   wherein the spacing value is a harmonic spacing value describing        a spacing between harmonics.

Another embodiment may have a decoder for decoding an encoded audiosignal, wherein the decoder is configured to decode the encoded audiosignal in a transform domain or filter-bank domain, wherein the decoderis configured to parse the encoded audio signal to acquire encodedspectral coefficients of the audio signal for a current frame and atleast one previous frame, and wherein the decoder is configured toselectively apply predictive decoding to a plurality of individualencoded spectral coefficients or groups of encoded spectralcoefficients, wherein the decoder is configured to acquire a spacingvalue, wherein the decoder is configured to select the plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients to which predictive decoding is applied based on thespacing value; wherein the spacing value is a harmonic spacing valuedescribing a spacing between harmonics.

Another embodiment may have an encoder for encoding an audio signal,wherein the encoder is configured to encode the audio signal in atransform domain or filter-bank domain, wherein the encoder isconfigured to determine spectral coefficients of the audio signal for acurrent frame and at least one previous frame, wherein the encoder isconfigured to selectively apply predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the encoder is configured to determine a spacing value, whereinthe encoder is configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the encoder isconfigured to predictively encode the plurality of individual spectralcoefficients or the groups of spectral coefficients of the currentframe, by coding prediction errors between a plurality of predictedindividual spectral coefficients or groups of predicted spectralcoefficients of the current frame and the plurality of individualspectral coefficients or groups of spectral coefficients of the currentframe; wherein the encoder is configured to derive predictioncoefficients from the spacing value, and wherein the encoder isconfigured to calculate the plurality of predicted individual spectralcoefficients or groups of predicted spectral coefficients for thecurrent frame using a corresponding plurality of individual spectralcoefficients or corresponding groups of spectral coefficients of atleast two previous frames and using the derived prediction coefficients;and wherein the encoder is configured to select spectral coefficients,spectral indices of which are equal to or lie within a range around aplurality of spectral indices derived on the basis of the spacing value,for a predictive encoding.

Yet another embodiment may have an encoder for encoding an audio signal,wherein the encoder is configured to encode the audio signal in atransform domain or filter-bank domain, wherein the encoder isconfigured to determine spectral coefficients of the audio signal for acurrent frame and at least one previous frame, wherein the encoder isconfigured to selectively apply predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the encoder is configured to determine a spacing value, whereinthe encoder is configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the encoder isconfigured to predictively encode the plurality of individual spectralcoefficients or the groups of spectral coefficients of the currentframe, by coding prediction errors between a plurality of predictedindividual spectral coefficients or groups of predicted spectralcoefficients of the current frame and the plurality of individualspectral coefficients or groups of spectral coefficients of the currentframe; wherein the encoder is configured to determine the plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients for the current frame using correspondingquantized versions of the plurality of individual spectral coefficientsor the groups of spectral coefficients of the previous frame; whereinthe encoder is configured to derive prediction coefficients from thespacing value, and wherein the encoder is configured to calculate theplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients for the current frame usingcorresponding quantized versions of the plurality of individual spectralcoefficients or the groups of spectral coefficients of at least twoprevious frames and using the derived prediction coefficients; andwherein the encoder is configured to select spectral coefficients,spectral indices of which are equal to or lie within a range around aplurality of spectral indices derived on the basis of the spacing value,for a predictive encoding.

Another embodiment may have an encoder for encoding an audio signal,wherein the encoder is configured to encode the audio signal in atransform domain or filter-bank domain, wherein the encoder isconfigured to determine spectral coefficients of the audio signal for acurrent frame and at least one previous frame, wherein the encoder isconfigured to selectively apply predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the encoder is configured to determine a spacing value, whereinthe encoder is configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the encoder isconfigured to determine an instantaneous fundamental frequency of theaudio signal and to derive the spacing value from the instantaneousfundamental frequency or a fraction or a multiple thereof.

Yet another embodiment may have an encoder for encoding an audio signal,wherein the encoder is configured to encode the audio signal in atransform domain or filter-bank domain, wherein the encoder isconfigured to determine spectral coefficients of the audio signal for acurrent frame and at least one previous frame, wherein the encoder isconfigured to selectively apply predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the encoder is configured to determine a spacing value, whereinthe encoder is configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the encoder isconfigured to select individual spectral coefficients or groups ofspectral coefficients spectrally arranged according to a harmonic griddefined by the spacing value for a predictive encoding.

Another embodiment may have an encoder for encoding an audio signal,wherein the encoder is configured to encode the audio signal in atransform domain or filter-bank domain, wherein the encoder isconfigured to determine spectral coefficients of the audio signal for acurrent frame and at least one previous frame, wherein the encoder isconfigured to selectively apply predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the encoder is configured to determine a spacing value, whereinthe encoder is configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the audio signalhas at least two harmonic signal components, wherein the encoder isconfigured to apply predictive encoding only to those plurality ofindividual spectral coefficients or groups of spectral coefficientswhich represent the at least two harmonic signal components or spectralenvironments around the at least two harmonic signal components of theaudio signal.

Another embodiment may have a decoder for decoding an encoded audiosignal, wherein the decoder is configured to decode the encoded audiosignal in a transform domain or filter-bank domain, wherein the decoderis configured to parse the encoded audio signal to acquire encodedspectral coefficients of the audio signal for a current frame and atleast one previous frame, and wherein the decoder is configured toselectively apply predictive decoding to a plurality of individualencoded spectral coefficients or groups of encoded spectralcoefficients, wherein the decoder is configured to acquire a spacingvalue, wherein the decoder is configured to select the plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients to which predictive decoding is applied based on thespacing value; wherein the decoder is configured to entropy decode theencoded spectral coefficients, to acquire quantized prediction errorsfor the spectral coefficients to which predictive decoding is to beapplied and quantized spectral coefficients for spectral coefficients towhich predictive decoding is not to be applied; wherein the decoder isconfigured to apply the quantized prediction errors to a plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients, to acquire, for the current frame, decodedspectral coefficients associated with the encoded spectral coefficientsto which predictive decoding is applied; wherein the decoder isconfigured to determine the plurality of predicted individual spectralcoefficients or groups of predicted spectral coefficients for thecurrent frame based on a corresponding plurality of the individualencoded spectral coefficients or groups of encoded spectral coefficientsof the previous frame; wherein the decoder is configured to deriveprediction coefficients from the spacing value, and wherein the decoderis configured to calculate the plurality of predicted individualspectral coefficients or groups of predicted spectral coefficients forthe current frame using a corresponding plurality of previously decodedindividual spectral coefficients or groups of previously decodedspectral coefficients of at least two previous frames and using thederived prediction coefficients; wherein the decoder is configured toselect spectral coefficients, spectral indices of which are equal to orlie within a range around a plurality of spectral indices derived on thebasis of the spacing value, for a predictive decoding.

Another embodiment may have a decoder for decoding an encoded audiosignal, wherein the decoder is configured to decode the encoded audiosignal in a transform domain or filter-bank domain, wherein the decoderis configured to parse the encoded audio signal to acquire encodedspectral coefficients of the audio signal for a current frame and atleast one previous frame, and wherein the decoder is configured toselectively apply predictive decoding to a plurality of individualencoded spectral coefficients or groups of encoded spectralcoefficients, wherein the decoder is configured to acquire a spacingvalue, wherein the decoder is configured to select the plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients to which predictive decoding is applied based on thespacing value; wherein the decoder is configured to select individualspectral coefficients or groups of spectral coefficients spectrallyarranged according to a harmonic grid defined by the spacing value for apredictive decoding.

Yet another embodiment may have a decoder for decoding an encoded audiosignal, wherein the decoder is configured to decode the encoded audiosignal in a transform domain or filter-bank domain, wherein the decoderis configured to parse the encoded audio signal to acquire encodedspectral coefficients of the audio signal for a current frame and atleast one previous frame, and wherein the decoder is configured toselectively apply predictive decoding to a plurality of individualencoded spectral coefficients or groups of encoded spectralcoefficients, wherein the decoder is configured to acquire a spacingvalue, wherein the decoder is configured to select the plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients to which predictive decoding is applied based on thespacing value; wherein the decoder is configured to determine thespacing value; and wherein the decoder is configured to determine aninstantaneous fundamental frequency and to derive the spacing value fromthe instantaneous fundamental frequency or a fraction or a multiplethereof.

Another embodiment may have a decoder for decoding an encoded audiosignal, wherein the decoder is configured to decode the encoded audiosignal in a transform domain or filter-bank domain, wherein the decoderis configured to parse the encoded audio signal to acquire encodedspectral coefficients of the audio signal for a current frame and atleast one previous frame, and wherein the decoder is configured toselectively apply predictive decoding to a plurality of individualencoded spectral coefficients or groups of encoded spectralcoefficients, wherein the decoder is configured to acquire a spacingvalue, wherein the decoder is configured to select the plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients to which predictive decoding is applied based on thespacing value; wherein the audio signal represented by the encoded audiosignal has at least two harmonic signal components, wherein the decoderis configured to apply predictive decoding only to those plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients which represent the at least two harmonic signal componentsor spectral environments around the at least two harmonic signalcomponents of the audio signal.

Another embodiment may have a decoder for decoding an encoded audiosignal, wherein the decoder is configured to decode the encoded audiosignal in a transform domain or filter-bank domain, wherein the decoderis configured to parse the encoded audio signal to acquire encodedspectral coefficients of the audio signal for a current frame and atleast one previous frame, and wherein the decoder is configured toselectively apply predictive decoding to a plurality of individualencoded spectral coefficients or groups of encoded spectralcoefficients, wherein the decoder is configured to acquire a spacingvalue, wherein the decoder is configured to select the plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients to which predictive decoding is applied based on thespacing value; wherein the encoded audio signal has the spacing value oran encoded version thereof, wherein the spacing value is a harmonicspacing value describing a spacing between harmonics, the harmonicspacing value indicating those plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients which representat least two harmonic signal components of the audio signal.

According to another embodiment, a method for encoding an audio signalin a transform domain or filter-bank domain may have the steps of:determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value; andselectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value; wherein the spacing value is a harmonic spacingvalue describing a spacing between harmonics.

According to another embodiment, a method for encoding an audio signalin a transform domain or filter-bank domain may have the steps of:determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value;selectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value, wherein the plurality of individual spectralcoefficients or the groups of spectral coefficients of the current frameare predictively encoded, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; deriving prediction coefficients from the spacingvalue; calculating the plurality of predicted individual spectralcoefficients or groups of predicted spectral coefficients for thecurrent frame using a corresponding plurality of individual spectralcoefficients or corresponding groups of spectral coefficients of atleast two previous frames and using the derived prediction coefficients;and selecting spectral coefficients, spectral indices of which are equalto or lie within a range around a plurality of spectral indices derivedon the basis of the spacing value, for a predictive encoding.

According to yet another embodiment, a method for encoding an audiosignal in a transform domain or filter-bank domain may have the stepsof: determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value;selectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value; predictively encoding the plurality of individualspectral coefficients or the groups of spectral coefficients of thecurrent frame, by coding prediction errors between a plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients of the current frame and the plurality ofindividual spectral coefficients or groups of spectral coefficients ofthe current frame; determining the plurality of predicted individualspectral coefficients or groups of predicted spectral coefficients forthe current frame using corresponding quantized versions of theplurality of individual spectral coefficients or the groups of spectralcoefficients of the previous frame; deriving prediction coefficientsfrom the spacing value; calculating the plurality of predictedindividual spectral coefficients or groups of predicted spectralcoefficients for the current frame using corresponding quantizedversions of the plurality of individual spectral coefficients or thegroups of spectral coefficients of at least two previous frames andusing the derived prediction coefficients; selecting spectralcoefficients, spectral indices of which are equal to or lie within arange around a plurality of spectral indices derived on the basis of thespacing value, for a predictive encoding.

According to another embodiment, a method for encoding an audio signalin a transform domain or filter-bank domain may have the steps of:determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value;selectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value; determining an instantaneous fundamental frequencyof the audio signal; deriving the spacing value from the instantaneousfundamental frequency or a fraction or a multiple thereof.

According to another embodiment, a method for encoding an audio signalin a transform domain or filter-bank domain may have the steps of:determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value;selectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value; and selecting individual spectral coefficients orgroups of spectral coefficients spectrally arranged according to aharmonic grid defined by the spacing value for a predictive encoding.

According to another embodiment, a method for encoding an audio signalin a transform domain or filter-bank domain may have the steps of:determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value;selectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value; wherein the audio signal has at least two harmonicsignal components; applying predictive encoding only to those pluralityof individual spectral coefficients or groups of spectral coefficientswhich represent the at least two harmonic signal components or spectralenvironments around the at least two harmonic signal components of theaudio signal.

According to another embodiment, a method for decoding an encoded audiosignal in a transform domain or filter-bank domain may have the stepsof: parsing the encoded audio signal to acquire encoded spectralcoefficients of the audio signal for a current frame and at least oneprevious frame; acquiring a spacing value; and selectively applyingpredictive decoding to a plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients, wherein theplurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients to which predictive decoding is appliedare selected based on the spacing value; wherein the spacing value is aharmonic spacing value describing a spacing between harmonics.

According to another embodiment, a method for decoding an encoded audiosignal in a transform domain or filter-bank domain may have the stepsof: parsing the encoded audio signal to acquire encoded spectralcoefficients of the audio signal for a current frame and at least oneprevious frame; acquiring a spacing value; and selectively applyingpredictive decoding to a plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients, wherein theplurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients to which predictive decoding is appliedare selected based on the spacing value; entropy decoding the encodedspectral coefficients, to acquire quantized prediction errors for thespectral coefficients to which predictive decoding is to be applied andquantized spectral coefficients for spectral coefficients to whichpredictive decoding is not to be applied; applying the quantizedprediction errors to a plurality of predicted individual spectralcoefficients or groups of predicted spectral coefficients, to acquire,for the current frame, decoded spectral coefficients associated with theencoded spectral coefficients to which predictive decoding is applied;determining the plurality of predicted individual spectral coefficientsor groups of predicted spectral coefficients for the current frame basedon a corresponding plurality of the individual encoded spectralcoefficients or groups of encoded spectral coefficients of the previousframe; deriving prediction coefficients from the spacing value;calculating the plurality of predicted individual spectral coefficientsor groups of predicted spectral coefficients for the current frame usinga corresponding plurality of previously decoded individual spectralcoefficients or groups of previously decoded spectral coefficients of atleast two previous frames and using the derived prediction coefficients;and selecting spectral coefficients, spectral indices of which are equalto or lie within a range around a plurality of spectral indices derivedon the basis of the spacing value, for a predictive decoding.

According to another embodiment, a method for decoding an encoded audiosignal in a transform domain or filter-bank domain may have the stepsof: parsing the encoded audio signal to acquire encoded spectralcoefficients of the audio signal for a current frame and at least oneprevious frame; acquiring a spacing value; and selectively applyingpredictive decoding to a plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients, wherein theplurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients to which predictive decoding is appliedare selected based on the spacing value; selecting individual spectralcoefficients or groups of spectral coefficients spectrally arrangedaccording to a harmonic grid defined by the spacing value for apredictive decoding.

According to another embodiment, a method for decoding an encoded audiosignal in a transform domain or filter-bank domain, may have the stepsof: parsing the encoded audio signal to acquire encoded spectralcoefficients of the audio signal for a current frame and at least oneprevious frame; acquiring a spacing value; and selectively applyingpredictive decoding to a plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients, wherein theplurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients to which predictive decoding is appliedare selected based on the spacing value; determining the spacing value;determining an instantaneous fundamental frequency; and deriving thespacing value from the instantaneous fundamental frequency or a fractionor a multiple thereof.

According to another embodiment, a method for decoding an encoded audiosignal in a transform domain or filter-bank domain may have the stepsof: parsing the encoded audio signal to acquire encoded spectralcoefficients of the audio signal for a current frame and at least oneprevious frame; acquiring a spacing value; and selectively applyingpredictive decoding to a plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients, wherein theplurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients to which predictive decoding is appliedare selected based on the spacing value; wherein the audio signalrepresented by the encoded audio signal has at least two harmonic signalcomponents; applying predictive decoding only to those plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients which represent the at least two harmonic signal componentsor spectral environments around the at least two harmonic signalcomponents of the audio signal.

According to another embodiment, a method for decoding an encoded audiosignal in a transform domain or filter-bank domain may have the stepsof: parsing the encoded audio signal to acquire encoded spectralcoefficients of the audio signal for a current frame and at least oneprevious frame; acquiring a spacing value; and selectively applyingpredictive decoding to a plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients, wherein theplurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients to which predictive decoding is appliedare selected based on the spacing value; wherein the encoded audiosignal has the spacing value or an encoded version thereof, wherein thespacing value is a harmonic spacing value describing a spacing betweenharmonics, the harmonic spacing value indicating those plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients which represent at least two harmonic signal components ofthe audio signal.

According to another embodiment, a non-transitory digital storage mediummay have a computer program stored thereon to perform any of theinventive methods when said computer program is run by a computer.

Embodiments provide an encoder for encoding an audio signal. The encoderis configured to encode the audio signal in a transform domain orfilter-bank domain, wherein the encoder is configured to determinespectral coefficients of the audio signal for a current frame and atleast one previous frame, wherein the encoder is configured toselectively apply predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theencoder is configured to determine a spacing value, wherein the encoderis configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value which may be transmittedas side information with the encoded audio signal.

Further embodiments provide a decoder for decoding an encoded audiosignal (e.g., encoded with the above described encoder). The decoder isconfigured to decode the encoded audio signal in a transform domain orfilter-bank domain, wherein the decoder is configured to parse theencoded audio signal to obtain encoded spectral coefficients of theaudio signal for a current frame and at least one previous frame, andwherein the decoder is configured to selectively apply predictivedecoding to a plurality of individual encoded spectral coefficients orgroups of encoded spectral coefficients, wherein the decoder may beconfigured to select the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients to whichpredictive decoding is applied based on a transmitted spacing value.

According to the concept of the present invention, predictive encodingis (only) applied to selected spectral coefficients. The spectralcoefficients to which predictive encoding is applied can be selected independence on signal characteristics. For example, by not applyingpredictive encoding to noisy signal components the aforementioned errorsintroduced by predicting non-predictable noisy signal components areavoided. At the same time computational complexity can be reduced sincepredictive encoding is only applied to selected spectral components.

For example, perceptual coding of tonal audio signals can be performed(e.g., by the encoder) by means of transform coding with guided/adaptivespectral-domain inter-frame prediction methods. The efficiency offrequency domain prediction (FDP) can be increased, and thecomputational complexity can be reduced, by applying the prediction onlyto spectral coefficients, for example, around harmonic signal componentslocated at integer multiples of a fundamental frequency or pitch, whichcan be signaled in an appropriate bit-stream from an encoder to adecoder, e.g. as a spacing value. Embodiments of the present inventioncan be advantageously implemented or integrated into the MPEG-H 3D audiocodec, but are applicable to any audio transform coding system, such as,e.g., MPEG-2 AAC.

Further embodiments provide a method for encoding an audio signal in atransform domain or filter-bank domain, the method comprises:

-   -   determining spectral coefficients of the audio signal for a        current frame and at least one previous frame;    -   determining a spacing value; and    -   selectively applying predictive encoding to a plurality of        individual spectral coefficients or groups of spectral        coefficients, wherein the plurality of individual spectral        coefficients or groups of spectral coefficients to which        predictive encoding is applied are selected based on the spacing        value.

Further embodiments provide a method for decoding an encoded audiosignal in a transform domain or filter-bank domain, the methodcomprises:

-   -   parsing the encoded audio signal to obtain encoded spectral        coefficients of the audio signal for a current frame and at        least one previous frame;    -   obtaining a spacing value; and    -   selectively applying predictive decoding to a plurality of        individual encoded spectral coefficients or groups of encoded        spectral coefficients, wherein the plurality of individual        encoded spectral coefficients or groups of encoded spectral        coefficients to which predictive decoding is applied are        selected based on the spacing value.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be detailed subsequentlyreferring to the appended drawings, in which:

FIG. 1 shows a schematic block diagram of an encoder for encoding anaudio signal, according to an embodiment;

FIG. 2 shows in a diagram an amplitude of an audio signal plotted overfrequency for a current frame and corresponding selected spectralcoefficients to which predictive encoding is applied, according to anembodiment;

FIG. 3 shows in a diagram an amplitude of an audio signal plotted overfrequency for a current frame and corresponding spectral coefficientswhich are subjected to prediction according to MPEG-2 AAC;

FIG. 4 shows a schematic block diagram of a decoder for decoding anencoded audio signal, according to an embodiment;

FIG. 5 shows a flowchart of a method for encoding an audio signal,according to an embodiment; and

FIG. 6 shows a flowchart of a method for decoding an encoded audiosignal, according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Equal or equivalent elements or elements with equal or equivalentfunctionality are denoted in the following description by equal orequivalent reference numerals.

In the following description, a plurality of details are set forth toprovide a more thorough explanation of embodiments of the presentinvention. However, it will be apparent to one skilled in the art thatembodiments of the present invention may be practiced without thesespecific details. In other instances, well-known structures and devicesare shown in block diagram form rather than in detail in order to avoidobscuring embodiments of the present invention. In addition, features ofthe different embodiments described hereinafter may be combined witheach other unless specifically noted otherwise.

FIG. 1 shows a schematic block diagram of an encoder 100 for encoding anaudio signal 102, according to an embodiment. The encoder 100 isconfigured to encode the audio signal 102 in a transform domain orfilter-bank domain 104 (e.g., frequency domain, or spectral domain),wherein the encoder 100 is configured to determine spectral coefficients106_t 0_f 1 to 106_t 0_f 6 of the audio signal 102 for a current frame108_t 0 and spectral coefficients 106_t-1_f 1 to 106_t-1_f 6 of theaudio signal for at least one previous frame 108_t-1. Further, theencoder 100 is configured to selectively apply predictive encoding to aplurality of individual spectral coefficients 106_t 0_f 2 or groups ofspectral coefficients 106_t 0_f 4 and 106_t 0_f 5, wherein the encoder100 is configured to determine a spacing value, wherein the encoder 100is configured to select the plurality of individual spectralcoefficients 106_t 0_f 2 or groups of spectral coefficients 106_t 0_f 4and 106_t 0_f 5 to which predictive encoding is applied based on thespacing value.

In other words, the encoder 100 is configured to selectively applypredictive encoding to a plurality of individual spectral coefficients106_t 0_f 2 or groups of spectral coefficients 106_t 0_f 4 and 106_t 0_f5 selected based on a single spacing value transmitted as sideinformation.

This spacing value may correspond to a frequency (e.g. a fundamentalfrequency of a harmonic tone (of the audio signal 102)), which definestogether with its integer multiples the centers of all groups ofspectral coefficients for which prediction is applied: The first groupcan be centered around this frequency, the second group can be centeredaround this frequency multiplied by two, the third group can be centeredaround this frequency multiplied by three, and so on. The knowledge ofthese center frequencies enables the calculation of predictioncoefficients for predicting corresponding sinusoidal signal components(e.g. fundamental and overtones of harmonic signals). Thus, complicatedand error prone backward adaptation of prediction coefficients is nolonger needed.

In embodiments, the encoder 100 can be configured to determine onespacing value per frame.

In embodiments, the plurality of individual spectral coefficients 106_t0_f 2 or groups of spectral coefficients 106_t 0_f 4 and 106_t 0_f 5 canbe separated by at least one spectral coefficient 106_t 0_f 3.

In embodiments, the encoder 100 can be configured to apply thepredictive encoding to a plurality of individual spectral coefficientswhich are separated by at least one spectral coefficient, such as to twoindividual spectral coefficients which are separated by at least onespectral coefficient. Further, the encoder 100 can be configured toapply the predictive encoding to a plurality of groups of spectralcoefficients (each of the groups comprising at least two spectralcoefficients) which are separated by at least one spectral coefficient,such as to two groups of spectral coefficients which are separated by atleast one spectral coefficient. Further, the encoder 100 can beconfigured to apply the predictive encoding to a plurality of individualspectral coefficients and/or groups of spectral coefficients which areseparated by at least one spectral coefficient, such as to at least oneindividual spectral coefficient and at least one group of spectralcoefficients which are separated by at least one spectral coefficient.

In the example shown in FIG. 1, the encoder 100 is configured todetermine six spectral coefficients 106_t 0_f 1 to 106_t 0_f 6 for thecurrent frame 108_t 0 and six spectral coefficients 106_t-1_f 1 to106_t-1_f 6 for the previous frame 108_t-1. Thereby, the encoder 100 isconfigured to selectively apply predictive encoding to the individualsecond spectral coefficient 106_t 0_f 2 of the current frame and to thegroup of spectral coefficients consisting of the fourth and fifthspectral coefficients 106_t 0_f 4 and 106_t 0_f 5 of the current frame108_t 0. As can be seen, the individual second spectral coefficient106_t 0_f 2 and the group of spectral coefficients consisting of thefourth and fifth spectral coefficients 106_t 0_f 4 and 106_t 0_f 5 areseparated from each other by the third spectral coefficient 106_t 0_f 3.

Note that the term “selectively” as used herein refers to applyingpredictive encoding (only) to selected spectral coefficients. In otherwords, predictive encoding is not necessarily applied to all spectralcoefficients, but rather only to selected individual spectralcoefficients or groups of spectral coefficients, the selected individualspectral coefficients and/or groups of spectral coefficients which canbe separated from each other by at least one spectral coefficient. Inother words, predictive encoding can be disabled for at least onespectral coefficient by which the selected plurality of individualspectral coefficients or groups of spectral coefficients are separated.

In embodiments, the encoder 100 can be configured to selectively applypredictive encoding to a plurality of individual spectral coefficients106_t 0_f 2 or groups of spectral coefficients 106_t 0_f 4 and 106_t 0_f5 of the current frame 108_t 0 based on at least a correspondingplurality of individual spectral coefficients 106_t-1_f 2 or groups ofspectral coefficients 106_t-1_f 4 and 106_t-1_f 5 of the previous frame108_t-1.

For example, the encoder 100 can be configured to predictively encodethe plurality of individual spectral coefficients 106_t 0_f 2 or thegroups of spectral coefficients 106_t 0_f 4 and 106_t 0_f 5 of thecurrent frame 108_t 0, by coding prediction errors between a pluralityof predicted individual spectral coefficients 110_t 0_f 2 or groups ofpredicted spectral coefficients 110_t 0_f 4 and 110_t 0_f 5 of thecurrent frame 108_t 0 and the plurality of individual spectralcoefficients 106_t 0_f 2 or groups of spectral coefficients 106_t 0_f 4and 106_t 0_f 5 of the current frame (or quantized versions thereof).

In FIG. 1, the encoder 100 encodes the individual spectral coefficient106_t 0_f 2 and the group of spectral coefficients consisting of thespectral coefficients 106_t 0_f 4 and 106_t 0_f 5, by coding aprediction errors between the predicted individual spectral coefficient110_t 0_f 2 of the current frame 108_t 0 and the individual spectralcoefficient 106_t 0_f 2 of the current frame 108_t 0 and between thegroup of predicted spectral coefficients 110_t 0_f 4 and 110_t 0_f 5 ofthe current frame and the group of spectral coefficients 106_t 0_f 4 and106_t 0_f 5 of the current frame.

In other words, the second spectral coefficient 106_t 0_f 2 is coded bycoding the prediction error (or difference) between the predicted secondspectral coefficient 110_t 0_f 2 and the (actual or determined) secondspectral coefficient 106_t 0_f 2, wherein the fourth spectralcoefficient 106_t 0_f 4 is coded by coding the prediction error (ordifference) between the predicted fourth spectral coefficient 110_t 0_f4 and the (actual or determined) fourth spectral coefficient 106_t 0_f 4and wherein the fifth spectral coefficient 106_t 0_f 5 is coded bycoding the prediction error (or difference) between the predicted fifthspectral coefficient 110_t 0_f 5 and the (actual or determined) fifthspectral coefficient 106_t 0_f 5.

In an embodiment, the encoder 100 can be configured to determine theplurality of predicted individual spectral coefficients 110_t 0_f 2 orgroups of predicted spectral coefficients 110_t 0_f 4 and 110_t 0_f 5for the current frame 108_t 0 by means of corresponding actual versionsof the plurality of individual spectral coefficients 106_t-1_f 2 or ofthe groups of spectral coefficients 106_t-1_f 4 and 106_t-1_f 5 of theprevious frame 108_t-1.

In other words, the encoder 100 may, in the above-describeddetermination process, use directly the plurality of actual individualspectral coefficients 106_t-1_f 2 or the groups of actual spectralcoefficients 106_t-1_f 4 and 106_t-1_f 5 of the previous frame 108_t-1,where the 106_t-1_f 2, 106_t-1_f 4 and 106_t-1_f 5 represent theoriginal, not yet quantized spectral coefficients or groups of spectralcoefficients, respectively, as they are obtained by the encoder 100 suchthat said encoder may operate in the transform domain or filter-bankdomain 104.

For example, the encoder 100 can be configured to determine the secondpredicted spectral coefficient 110_t 0_f 2 of the current frame 108_t 0based on a corresponding not yet quantized version of the secondspectral coefficient 106_t-1_f 2 of the previous frame 10 108_t-1, thepredicted fourth spectral coefficient 110_t 0_f 4 of the current frame108_t 0 based on a corresponding not yet quantized version of the fourthspectral coefficient 106_t-1_f 4 of the previous frame 108_t-1, and thepredicted fifth spectral coefficient 110_t 0_f 5 of the current frame108_t 0 based on a corresponding not yet quantized version of the fifthspectral coefficient 106_t-1_f 5 of the previous frame.

By way of this approach, the predictive encoding and decoding scheme canexhibit a kind of harmonic shaping of the quantization noise, since acorresponding decoder, an embodiment of which is described later withrespect to FIG. 4, can only employ, in the above-noted determinationstep, the transmitted quantized versions of the plurality of individualspectral coefficients 106_t-1_f 2 or of the plurality of groups ofspectral coefficients 106_t-1_f 4 and 106_t-1_f 5 of the previous frame108_t-1 for a predictive decoding.

While such harmonic noise shaping, as it is, for example, traditionallyperformed by long-term prediction (LTP) in the time domain, can besubjectively advantageous for predictive coding, in some cases it may beundesirable since it may lead to an unwanted, excessive amount oftonality introduced into a decoded audio signal. For this reason, analternative predictive encoding scheme, which is fully synchronized withthe corresponding decoding and, as such, only exploits any possibleprediction gains but does not lead to quantization noise shaping, isdescribed hereafter. According to this alternative encoding embodiment,the encoder 100 can be configured to determine the plurality ofpredicted individual spectral coefficients 110_t 0_f 2 or groups ofpredicted spectral coefficients 110_t 0_f 4 and 110_t 0_f 5 for thecurrent frame 108_t 0 using corresponding quantized versions of theplurality of individual spectral coefficients 106_t-1_f 2 or the groupsof spectral coefficients 106_t-1_f 4 and 106_t-1_f 5 of the previousframe 108_t-1.

For example, the encoder 100 can be configured to determine the secondpredicted spectral coefficient 110_t 0_f 2 of the current frame 108_t 0based on a corresponding quantized version of the second spectralcoefficient 106_t-1_f 2 of the previous frame 108_t-1, the predictedfourth spectral coefficient 110_t 0_f 4 of the current frame 108_t 0based on a corresponding quantized version of the fourth spectralcoefficient 106_t-1_f 4 of the previous frame 108_t-1, and the predictedfifth spectral coefficient 110_t 0_f 5 of the current frame 108_t 0based on a corresponding quantized version of the fifth spectralcoefficient 106_t-1_f 5 of the previous frame.

Further, the encoder 100 can be configured to derive predictioncoefficients 112_f 2, 114_f 2, 112_f 4, 114_f 4, 112_f 5 and 114_f 5from the spacing value, and to calculate the plurality of predictedindividual spectral coefficients 110_t 0_f 2 or groups of predictedspectral coefficients 110_t 0_f 4 and 110_t 0_f 5 for the current frame108_t 0 using corresponding quantized versions of the plurality ofindividual spectral coefficients 106_t-1_f 2 and 106_t-2_f 2 or groupsof spectral coefficients 106_t-1_f 4, 106_t-2_f 4, 106_t-1_f 5, and106_t-2_f 5 of at least two previous frames 108_t-1 and 108_t-2 andusing the derived prediction coefficients 112_f 2, 114_f 2, 112_f 4,114_f 4, 112_f 5 and 114_f 5.

For example, the encoder 100 can be configured to derive predictioncoefficients 112_f 2 and 114_f 2 for the second spectral coefficient106_t 0_f 2 from the spacing value, to derive prediction coefficients112_f 4 and 114_f 4 for the fourth spectral coefficient 106_t 0_f 4 fromthe spacing value, and to derive prediction coefficients 112_f 5 and114_f 5 for the fifth spectral coefficient 106_t 0_f 5 from the spacingvalue.

For example, the derivation of prediction coefficients can be derivedthe following way: If the spacing value corresponds to a frequency f0 ora coded version thereof, the center frequency of the K-th group ofspectral coefficients for which prediction is enabled is fc=K*f0. If thesampling frequency is fs and the transform hop size (shift betweensuccessive frames) is N, the ideal predictor coefficients in the K-thgroup assuming a sinusoidal signal with frequency fc are:p1=2*cos(N*2*pi*fc/fs) and p2=−1.

If, for example, both spectral coefficients 106_t 0_f 4 and 106_t 0_f 5are within this group, the prediction coefficients are:112_f4=112_f5=2*cos(N*2*pi*fc/fs) and 114_f4=114_f5=−1.

For stability reasons, a damping factor d can be introduced leading tomodified prediction coefficients:112_f4′=112_f5′=d*2*cos(N*2*pi*fc/fs),114_f4′=114_f5′=d ².

Since the spacing value is transmitted in the coded audio signal 120,the decoder can derive exactly the same prediction coefficients 212_f4=212_f 5=2*cos(N*2*pi*fc/fs) and 114_f 4=114_f 5=−1. If a dampingfactor is used, the coefficients can be modified accordingly.

As indicated in FIG. 1, the encoder 100 can be configured to provide anencoded audio signal 120. Thereby, the encoder 100 can be configured toinclude in the encoded audio signal 120 quantized versions of theprediction errors for the plurality of individual spectral coefficients106_t 0_f 2 or groups of spectral coefficients 106_t 0_f 4 and 106_t 0_f5 to which predictive encoding is applied. Further, the encoder 100 canbe configured to not include the prediction coefficients 112_f 2 to114_f 5 in the encoded audio signal 120.

Thus, the encoder 100 may only use the prediction coefficients 112_f 2to 114_f 5 for calculating the plurality of predicted individualspectral coefficients 110_t 0_f 2 or groups of predicted spectralcoefficients 110_t 0_f 4 and 110_t 0_f 5 and therefrom the predictionerrors between the predicted individual spectral coefficient 110_t 0_f 2or group of predicted spectral coefficients 110_t 0_f 4 and 110_t 0_f 5and the individual spectral coefficient 106_t 0_f 2 or group ofpredicted spectral coefficients 110_t 0_f 4 and 110_t 0_f 5 of thecurrent frame, but will neither provide the individual spectralcoefficients 106_t 0_f 4 (or a quantized version thereof) or groups ofspectral coefficients 106_t 0_f 4 and 106_t 0_f 5 (or quantized versionsthereof) nor the prediction coefficients 112_f 2 to 114_f 5 in theencoded audio signal 120. Hence, a decoder, an embodiment of which isdescribed later with respect to FIG. 4, may derive the predictioncoefficients 112_f 2 to 114_f 5 for calculating the plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients for the current frame from the spacing value.

In other words, the encoder 100 can be configured to provide the encodedaudio signal 120 including quantized versions of the prediction errorsinstead of quantized versions of the plurality of individual spectralcoefficients 106_t 0_f 2 or of the groups of spectral coefficients 106_t0_f 4 and 106_t 0_f 5 for the plurality of individual spectralcoefficients 106_t 0_f 2 or groups of spectral coefficients 106_t 0_f 4and 106_t 0_f 5 to which predictive encoding is applied.

Further, the encoder 100 can be configured to provide the encoded audiosignal 102 including quantized versions of the spectral coefficients106_t 0_f 3 by which the plurality of individual spectral coefficients106_t 0_f 2 or groups of spectral coefficients 106_t 0_f 4 and 106_t 0_f5 are separated, such that there is an alternation of spectralcoefficients 106_t 0_f 2 or groups of spectral coefficients 106_t 0_f 4and 106_t 0_f 5 for which quantized versions of the prediction errorsare included in the encoded audio signal 120 and spectral coefficients106_t 0_f 3 or groups of spectral coefficients for which quantizedversions are provided without using predictive encoding.

In embodiments, the encoder 100 can be further configured to entropyencode the quantized versions of the prediction errors and the quantizedversions of the spectral coefficients 106_t 0_f 3 by which the pluralityof individual spectral coefficients 106_t 0_f 2 or groups of spectralcoefficients 106_t 0_f 4 and 106_t 0_f 5 are separated, and to includethe entropy encoded versions in the encoded audio signal 120 (instead ofthe non-entropy encoded versions thereof).

FIG. 2 shows in a diagram an amplitude of the audio signal 102 plottedover frequency for a current frame 108_t 0. Further, in FIG. 2, thespectral coefficients in the transform domain or filter-bank domaindetermined by the encoder 100 for the current frame 108_t 0 of the audiosignal 102 are indicated.

As shown in FIG. 2, the encoder 100 can be configured to selectivelyapply prediction encoding to a plurality of groups 116_1 to 116_6 ofspectral coefficients which are separated by at least one spectralcoefficient. In detail, in the embodiment shown in FIG. 2, the encoder100 selectively applies prediction encoding to six groups 116_1 to 116_6of spectral coefficients, wherein each of the first five groups 116_1 to116_5 of spectral coefficients includes three spectral coefficients(e.g., the second group 116_2 includes the spectral coefficients 106_t0_f 8, 106_t 0_f 9 and 106_t 0_f 10), wherein the sixth group 116_6 ofspectral coefficients includes two spectral coefficients. Thereby, thesix groups 116_1 to 116_6 of spectral coefficients are separated by(five) groups 118_1 to 118_5 of spectral coefficients to whichprediction encoding is not applied.

In other words, as indicated in FIG. 2, the encoder 100 can beconfigured to selectively apply prediction encoding to groups 116_1 to110_6 of spectral coefficients, such that there is an alternation ofgroups 116_1 to 116_6 of spectral coefficients to which predictionencoding is applied and groups 118_1 to 118_5 of spectral coefficientsto which prediction encoding is not applied.

In embodiments, the encoder 100 can be configured to determine a spacingvalue (indicated in FIG. 2 by the arrows 122_1 and 122_2), wherein theencoder 100 can be configured to select the plurality of groups 116_1 to116_6 of spectral coefficients (or the plurality of individual spectralcoefficients) to which predictive encoding is applied based on thespacing value.

The spacing value can be, for example, a spacing (or distance) betweentwo characteristic frequencies of the audio signal 102, such as thepeaks 124_1 and 124_2 of the audio signal. Further, the spacing valuecan be a an integer number of spectral coefficients (or indices ofspectral coefficients) approximating the spacing between the twocharacteristic frequencies of the audio signal. Naturally, the spacingvalue can also be a real number or a fraction or multiple of the integernumber of spectral coefficients describing the spacing between the twocharacteristic frequencies of the audio signal.

In embodiments, the encoder 100 can be configured to determine aninstantaneous fundamental frequency of the audio signal (102) and toderive the spacing value from the instantaneous fundamental frequency ora fraction or a multiple thereof.

For example, the first peak 124_1 of the audio signal 102 can be aninstantaneous fundamental frequency (or pitch, or first harmonic) of theaudio signal 102. Therefore, the encoder 100 can be configured todetermine the instantaneous fundamental frequency of the audio signal102 and to derive the spacing value from the instantaneous fundamentalfrequency or a fraction or a multiple thereof. In that case, the spacingvalue can be an integer number (or a fraction, or a multiple thereof) ofspectral coefficients approximating the spacing between theinstantaneous fundamental frequency 124_1 and a second harmonic 124_2 ofthe audio signal 102.

Naturally, the audio signal 102 may comprise more than two harmonics.For example, the audio signal 102 shown in FIG. 2 comprises sixharmonics 124_1 to 124_6 spectrally distributed such that the audiosignal 102 comprises at every integer multiple of the instantaneousfundamental frequency a harmonic. Naturally, it also possible that theaudio signal 102 does not comprise all but only some of the harmonics,such as the first, third and fifth harmonic.

In embodiments, the encoder 100 can be configured to select groups 116_1to 116_6 of spectral coefficients (or individual spectral coefficients)spectrally arranged according to a harmonic grid defined by the spacingvalue for a predictive encoding. Thereby, the harmonic grid defined bythe spacing value describes the periodic spectral distribution(equidistant spacing) of harmonics in the audio signal 102. In otherwords, the harmonic grid defined by the spacing value can be a sequenceof spacing values describing the equidistant spacing of harmonics of theaudio signal.

Further, the encoder 100 can be configured to select spectralcoefficients (e.g. only those spectral coefficients), spectral indicesof which are equal to or lie within a range (e.g. predetermined orvariable) around a plurality of spectral indices derived on the basis ofthe spacing value, for a predictive encoding.

From the spacing value the indices (or numbers) of the spectralcoefficients which represent the harmonics of the audio signal 102 canbe derived. For example, assuming that a fourth spectral coefficient106_t 0_f 4 represents the instantaneous fundamental frequency of theaudio signal 102 and assuming that the spacing value is five, thespectral coefficient having the index nine can be derived on the basisof the spacing value. As can be seen in FIG. 2, the so derived spectralcoefficient having the index nine, i.e. the ninth spectral coefficient106_t 0_f 9, represents the second harmonic. Similarly, the spectralcoefficients having the indices 14, 19, 24 and 29 can be derived,representing the third to sixth harmonics 124_3 to 124_6. However, notonly spectral coefficients having the indices which are equal to theplurality of spectral indices derived on the basis of the spacing valuemay be predictively encoded, but also spectral coefficients havingindices within a given range around the plurality of spectral indicesderived on the basis of the spacing value. For instance, as shown inFIG. 2, the range can be three, such that not a plurality of individualspectral coefficients are selected for prediction encoding, but rather aplurality of groups of spectral coefficients.

Further, the encoder 100 can be configured to select the groups 116_1 to116_6 of spectral coefficients (or plurality of individual spectralcoefficients) to which predictive encoding is applied such that there isa periodic alternation, periodic with a tolerance of +/−1 spectralcoefficient, between groups 116_1 to 116_6 of spectral coefficients (orthe plurality of individual spectral coefficients) to which predictiveencoding is applied and the spectral coefficients by which groups ofspectral coefficients (or the plurality of individual spectralcoefficients) to which predictive encoding is applied are separated. Thetolerance of +/−1 spectral coefficient may be used when a distancebetween two harmonics of the audio signal 102 is not equal to an integerspacing value (integer with respect to indices or numbers of spectralcoefficients) but rather to a fraction or multiple thereof. This canalso be seen in FIG. 2 since the arrows 122_1 to 122_6 do not alwayspoint exactly to the center or middle of the corresponding spectralcoefficients.

In other words, the audio signal 102 can comprise at least two harmonicsignal components 124_1 to 124_6, wherein the encoder 100 can beconfigured to selectively apply predictive encoding to those pluralityof groups 116_1 to 116_6 of spectral coefficients (or individualspectral coefficients) which represent the at least two harmonic signalcomponents 124_1 to 124_6 or spectral environments around the at leasttwo harmonic signal components 124_1 to 124_6 of the audio signal 102.The spectral environments around the at least two harmonic signalcomponents 124_1 to 124_6 can be, for example, +/−1, 2, 3, 4 or 5spectral components.

Thereby, the encoder 100 can be configured to not apply predictiveencoding to those groups 118_1 to 118_5 of spectral coefficients (orplurality of individual spectral coefficients) which do not representthe at least two harmonic signal components 124_1 to 124_6 or spectralenvironments of the at least two harmonic signal components 124_1 to124_6 of the audio signal 102. In other words, the encoder 100 can beconfigured to not apply predictive encoding to those plurality of groups118_1 to 118_5 of spectral coefficients (or individual spectralcoefficients) which belong to a non-tonal background noise betweensignal harmonics 124_1 to 124_6.

Further, the encoder 100 can be configured to determine a harmonicspacing value indicating a spectral spacing between the at least twoharmonic signal components 124_1 to 124_6 of the audio signal 102, theharmonic spacing value indicating those plurality of individual spectralcoefficients or groups of spectral coefficients which represent the atleast two harmonic signal components 124_1 to 124_6 of the audio signal102.

Furthermore, the encoder 100 can be configured to provide the encodedaudio signal 120 such that the encoded audio signal 120 includes thespacing value (e.g., one spacing value per frame) or (alternatively) aparameter from which the spacing value can be directly derived.

Embodiments of the present invention address the abovementioned twoissues of the FDP method by introducing a harmonic spacing value intothe FDP process, signaled from the encoder (transmitter) 100 to arespective decoder (receiver) such that both can operate in a fullysynchronized fashion. Said harmonic spacing value may serve as anindicator of an instantaneous fundamental frequency (or pitch) of one ormore spectra associated with a frame to be coded and identifies whichspectral bins (spectral coefficients) shall be predicted. Morespecifically, only those spectral coefficients around harmonic signalcomponents located (in terms of their indexing) at integer multiples ofthe fundamental pitch (as defined by the harmonic spacing value) shallbe subjected to the prediction. FIGS. 2 and 3 illustrate thispitch-adaptive prediction approach by means of a simple example, whereinFIG. 3 shows the operation of the state-of-the-art predictor in MPEG-2AAC, which does not predict only around a harmonic grid but subjectsevery spectral bin below a certain stop frequency to prediction, andwherein FIG. 2 depicts the same predictor with a modification accordingto an embodiment integrated to perform the prediction only on those“tonal” bins which are close to the harmonic spacing grid.

Comparing FIGS. 2 and 3 reveals two advantages of the modificationaccording to an embodiment, namely (1) much fewer spectral bins areincluded in the prediction process, reducing complexity (in the givenexample by roughly 40% since only three fifths of the bins arepredicted), and (2) the bins belonging to the non-tonal background noisebetween the signals harmonics are not affected by prediction, whichshould increase the efficiency of the prediction.

Note that the harmonic spacing value does not necessarily need tocorrespond to the actual instantaneous pitch of the input signal butthat it could represent a fraction or multiple of the true pitch if thisyields an overall improvement of the efficiency of the predictionprocess. In addition, it may be emphasized that the harmonic spacingvalue does not have to reflect an integer multiple of the bin indexingor bandwidth unit but may include a fraction of said units.

Subsequently, an advantageous implementation into an MPEG-style audiocoder is described.

The pitch-adaptive prediction is advantageously integrated into theMPEG-2 AAC [ISO/IEC 13818-7, “Information technology—Part 7: AdvancedAudio Coding (AAC),” 2006.] or, utilizing a similar predictor as in AAC,into the MPEG-H 3D audio codec [ISO/IEC 23008-3, “Informationtechnology—High efficiency coding, part 3: 3D audio,” 2015.]. Inparticular, a one-bit flag can be written to, and read from, arespective bit-stream for each frame and channel which is notindependently coded (for independent frame channels, the flag may not betransmitted since prediction can be disabled to ensure theindependence). If the flag is set to one, another 8 bits can be writtenand read. These 8 bits represent a quantized version of (e.g. an indexto) the harmonic spacing value for the given frame and channel.Employing the harmonic spacing value derived from the quantized versionusing either a linear or non-linear mapping function, the predictionprocess can be carried out in the manner according to an embodimentshown in FIG. 2. Advantageously, only bins located within a maximaldistance of 1.5 bins around the harmonic grid are subjected to theprediction. For example, if the harmonic spacing value indicates aharmonic line at bin index 47.11, then only the bins at indices 46, 47and 48 are predicted. Said maximal distance, however, could be specifieddifferently, either fixed a-priori for all channels and frames orseparately for each frame and channel based on the harmonic spacingvalue.

FIG. 4 shows a schematic block diagram of a decoder 200 for decoding anencoded signal 120. The decoder 200 is configured to decode the encodedaudio signal 120 in a transform domain or filter-bank domain 204,wherein the decoder 200 is configured to parse the encoded audio signal120 to obtain encoded spectral coefficients 206_t 0_21 to 206_t 0_26 ofthe audio signal for a current frame 208_t 0 and encoded spectralcoefficients 206_t-1_f 0 to 206_t-1_f 6 for at least one previous frame208_t-1, and wherein the decoder 200 is configured to selectively applypredictive decoding to a plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients which areseparated by at least one encoded spectral coefficient.

In embodiments, the decoder 200 can be configured to apply thepredictive decoding to a plurality of individual encoded spectralcoefficients which are separated by at least one encoded spectralcoefficient, such as to two individual encoded spectral coefficientswhich are separated by at least one encoded spectral coefficient.Further, the decoder 200 can be configured to apply the predictivedecoding to a plurality of groups of encoded spectral coefficients (eachof the groups comprising at least two encoded spectral coefficients)which are separated by at least one encoded spectral coefficients, suchas to two groups of encoded spectral coefficients which are separated byat least one encoded spectral coefficient. Further, the decoder 200 canbe configured to apply the predictive decoding to a plurality ofindividual encoded spectral coefficients and/or groups of encodedspectral coefficients which are separated by at least one encodedspectral coefficient, such as to at least one individual encodedspectral coefficient and at least one group of encoded spectralcoefficients which are separated by at least one encoded spectralcoefficient.

In the example shown in FIG. 4, the decoder 200 is configured todetermine six encoded spectral coefficients 206_t 0_21 to 206_t 0_26 forthe current frame 208_t 0 and six encoded spectral coefficients206_t-1_f 1 to 206_t-1_f 6 for the previous frame 208_t-1. Thereby, thedecoder 200 is configured to selectively apply predictive decoding tothe individual second encoded spectral coefficient 206_t 0_22 of thecurrent frame and to the group of encoded spectral coefficientsconsisting of the fourth and fifth encoded spectral coefficients 206_t0_24 and 206_t 0_25 of the current frame 208_t 0. As can be seen, theindividual second encoded spectral coefficient 206_t 0_22 and the groupof encoded spectral coefficients consisting of the fourth and fifthencoded spectral coefficients 206_t 0_24 and 206_t 0_25 are separatedfrom each other by the third encoded spectral coefficient 206_t 0_23.

Note that the term “selectively” as used herein refers to applyingpredictive decoding (only) to selected encoded spectral coefficients. Inother words, predictive decoding is not applied to all encoded spectralcoefficients, but rather only to selected individual encoded spectralcoefficients or groups of encoded spectral coefficients, the selectedindividual encoded spectral coefficients and/or groups of encodedspectral coefficients being separated from each other by at least oneencoded spectral coefficient. In other words, predictive decoding is notapplied to the at least one encoded spectral coefficient by which theselected plurality of individual encoded spectral coefficients or groupsof encoded spectral coefficients are separated.

In embodiments the decoder 200 can be configured to not apply thepredictive decoding to the at least one encoded spectral coefficient206_t 0_23 by which the individual encoded spectral coefficients 206_t0_22 or the group of spectral coefficients 206_t 0_24 and 206_t 0_25 areseparated.

The decoder 200 can be configured to entropy decode the encoded spectralcoefficients, to obtain quantized prediction errors for the spectralcoefficients 206_t 0_f 2, 2016_t 0_f 4 and 206_t 0_f 5 to whichpredictive decoding is to be applied and quantized spectral coefficients206_t 0_f 3 for the at least one spectral coefficient to whichpredictive decoding is not to be applied. Thereby, the decoder 200 canbe configured to apply the quantized prediction errors to a plurality ofpredicted individual spectral coefficients 210_t 0_f 2 or groups ofpredicted spectral coefficients 210_t 0_f 4 and 210_t 0_f 5, to obtain,for the current frame 208_t 0, decoded spectral coefficients associatedwith the encoded spectral coefficients 206_t 0_22, 206_t 0_f 4 and 206_t0_f 5 to which predictive decoding is applied.

For example, the decoder 200 can be configured to obtain a secondquantized prediction error for a second quantized spectral coefficient206_t 0_f 2 and to apply the second quantized prediction error to thepredicted second spectral coefficient 210_t 0_f 2, to obtain a seconddecoded spectral coefficient associated with the second encoded spectralcoefficient 206_t 0_f 2, wherein the decoder 200 can be configured toobtain a fourth quantized prediction error for a fourth quantizedspectral coefficient 206_t 0_f 4 and to apply the fourth quantizedprediction error to the predicted fourth spectral coefficient 210_t 0_f4, to obtain a fourth decoded spectral coefficient associated with thefourth encoded spectral coefficient 206_t 0_f 4, and wherein the decoder200 can be configured to obtain a fifth quantized prediction error for afifth quantized spectral coefficient 206_t 0_f 5 and to apply the fifthquantized prediction error to the predicted fifth spectral coefficient210_t 0_f 5, to obtain a fifth decoded spectral coefficient associatedwith the fifth encoded spectral coefficient 206_t 0_f 5.

Further, the decoder 200 can be configured to determine the plurality ofpredicted individual spectral coefficients 210_t 0_f 2 or groups ofpredicted spectral coefficients 210_t 0_f 4 and 210_t 0_f 5 for thecurrent frame 208_t 0 based on a corresponding plurality of theindividual encoded spectral coefficients 206_t-1_f 2 (e.g., using aplurality of previously decoded spectral coefficients associated withthe plurality of the individual encoded spectral coefficients 206_t-1_f2) or groups of encoded spectral coefficients 206_t-1_f 4 and 206_t-1_f5 (e.g., using groups of previously decoded spectral coefficientsassociated with the groups of encoded spectral coefficients 206_t-1_f 4and 206_t-1_f 5) of the previous frame 208_t-1.

For example, the decoder 200 can be configured to determine the secondpredicted spectral coefficient 210_t 0_f 2 of the current frame 208_t 0using a previously decoded (quantized) second spectral coefficientassociated with the second encoded spectral coefficient 206_t-1_f 2 ofthe previous frame 208_t-1, the fourth predicted spectral coefficient2102024 of the current frame 208_t 0 using a previously decoded(quantized) fourth spectral coefficient associated with the fourthencoded spectral coefficient 206_t-1_f 4 of the previous frame 208_t-1,and the fifth predicted spectral coefficient 210_t 0_25 of the currentframe 208_t 0 using a previously decoded (quantized) fifth spectralcoefficient associated with the fifth encoded spectral coefficient206_t-1_f 5 of the previous frame 208_t-1.

Furthermore, the decoder 200 can be configured to derive predictioncoefficients from the spacing value, and wherein the decoder 200 can beconfigured to calculate the plurality of predicted individual spectralcoefficients 210_t 0_f 2 or groups of predicted spectral coefficients210_t 0_f 4 and 210_t 0_f 5 for the current frame 208_t 0 using acorresponding plurality of previously decoded individual spectralcoefficients or groups of previously decoded spectral coefficients of atleast two previous frames 208_t-1 and 208_t-2 and using the derivedprediction coefficients.

For example, the decoder 200 can be configured to derive predictioncoefficients 212_f 2 and 214_f 2 for the second encoded spectralcoefficient 206_t 0_f 2 from the spacing value, to derive predictioncoefficients 212_f 4 and 214_f 4 for the fourth encoded spectralcoefficient 206_t 0_f 4 from the spacing value, and to derive predictioncoefficients 212_f 5 and 214_f 5 for the fifth encoded spectralcoefficient 206_t 0_f 5 from the spacing value.

Note that the decoder 200 can be configured to decode the encoded audiosignal 120 in order to obtain quantized prediction errors instead of aplurality of individual quantized spectral coefficients or groups ofquantized spectral coefficients for the plurality of individual encodedspectral coefficients or groups of encoded spectral coefficients towhich predictive decoding is applied.

Further, the decoder 200 can be configured to decode the encoded audiosignal 120 in order to obtain quantized spectral coefficients by whichthe plurality of individual spectral coefficients or groups of spectralcoefficients are separated, such that there is an alternation of encodedspectral coefficients 206_t 0_f 2 or groups of encoded spectralcoefficients 206_t 0_f 4 and 206_t 0_f 5 for which quantized predictionerrors are obtained and encoded spectral coefficients 206_t 0_f 3 orgroups of encoded spectral coefficients for which quantized spectralcoefficients are obtained.

The decoder 200 can be configured to provide a decoded audio signal 220using the decoded spectral coefficients associated with the encodedspectral coefficients 206_t 0_22, 206_t 0_f 4 and 206_t 0_f 5 to whichpredictive decoding is applied, and using entropy decoded spectralcoefficients associated with the encoded spectral coefficients 206_t0_21, 206_t 0_23 and 206_t 0_f 6 to which predictive decoding is notapplied.

In embodiments, the decoder 200 can be configured to obtain a spacingvalue, wherein the decoder 200 can be configured to select the pluralityof individual encoded spectral coefficients 206_t 0_f 2 or groups ofencoded spectral coefficients 206_t 0_24 and 206_t 0_25 to whichpredictive decoding is applied based on the spacing value.

As already mentioned above with respect to the description of thecorresponding encoder 100, the spacing value can be, for example, aspacing (or distance) between two characteristic frequencies of theaudio signal. Further, the spacing value can be a an integer number ofspectral coefficients (or indices of spectral coefficients)approximating the spacing between the two characteristic frequencies ofthe audio signal. Naturally, the spacing value can also be a fraction ormultiple of the integer number of spectral coefficients describing thespacing between the two characteristic frequencies of the audio signal.

The decoder 200 can be configured to select individual spectralcoefficients or groups of spectral coefficients spectrally arrangedaccording to a harmonic grid defined by the spacing value for apredictive decoding. The harmonic grid defined by the spacing value maydescribe the periodic spectral distribution (equidistant spacing) ofharmonics in the audio signal 102. In other words, the harmonic griddefined by the spacing value can be a sequence of spacing valuesdescribing the equidistant spacing of harmonics of the audio signal 102.

Furthermore, the decoder 200 can be configured to select spectralcoefficients (e.g. only those spectral coefficients), spectral indicesof which are equal to or lie within a range (e.g. predetermined orvariable range) around a plurality of spectral indices derived on thebasis of the spacing value, for a predictive decoding. Thereby, thedecoder 200 can be configured to set a width of the range in dependenceon the spacing value.

In embodiments, the encoded audio signal can comprise the spacing valueor an encoded version thereof (e.g., a parameter from which the spacingvalue can be directly derived), wherein the decoder 200 can beconfigured to extract the spacing value or the encoded version thereoffrom the encoded audio signal to obtain the spacing value.

Alternatively, the decoder 200 can be configured to determine thespacing value by itself, i.e. the encoded audio signal does not includethe spacing value. In that case, the decoder 200 can be configured todetermine an instantaneous fundamental frequency (of the encoded audiosignal 120 representing the audio signal 102) and to derive the spacingvalue from the instantaneous fundamental frequency or a fraction or amultiple thereof.

In embodiments, the decoder 200 can be configured to select theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive decoding is applied such that there isa periodic alternation, periodic with a tolerance of +/−1 spectralcoefficient, between the plurality of individual spectral coefficientsor groups of spectral coefficients to which predictive decoding isapplied and the spectral coefficients by which the plurality ofindividual spectral coefficients or groups of spectral coefficients towhich predictive decoding is applied are separated.

In embodiments, the audio signal 102 represented by the encoded audiosignal 120 comprises at least two harmonic signal components, whereinthe decoder 200 is configured to selectively apply predictive decodingto those plurality of individual encoded spectral coefficients 206_t 0_f2 or groups of encoded spectral coefficients 206_t 0_24 and 206_t 0_25which represent the at least two harmonic signal components or spectralenvironments around the at least two harmonic signal components of theaudio signal 102. The spectral environments around the at least twoharmonic signal components can be, for example, +/−1, 2, 3, 4 or 5spectral components.

Thereby, the decoder 200 can be configured to identify the at least twoharmonic signal components, and to selectively apply predictive decodingto those plurality of individual encoded spectral coefficients 206_t 0_f2 or groups of encoded spectral coefficients 206_t 0_f 4 and 206_t 0_f 5which are associated with the identified harmonic signal components,e.g., which represent the identified harmonic signal components or whichsurround the identified harmonic signal components).

Alternatively, the encoded audio signal 120 may comprise an information(e.g., the spacing value) identifying the at least two harmonic signalcomponents. In that case, the decoder 200 can be configured toselectively apply predictive decoding to those plurality of individualencoded spectral coefficients 206_t 0_f 2 or groups of encoded spectralcoefficients 206_t 0_f 4 and 206_t 0_f 5 which are associated with theidentified harmonic signal components, e.g., which represent theidentified harmonic signal components or which surround the identifiedharmonic signal components).

In both of the aforementioned alternatives, the decoder 200 can beconfigured to not apply predictive decoding to those plurality ofindividual encoded spectral coefficients 206_t 0_f 3, 206_t 0_f 1 and206_t 0_f 6 or groups of encoded spectral coefficients which do notrepresent the at least two harmonic signal components or spectralenvironments of the at least two harmonic signal components of the audiosignal 102.

In other words, the decoder 200 can be configured to not applypredictive decoding to those plurality of individual encoded spectralcoefficients 206_t 0_f 3, 206_t 0_f 1, 206_t 0_f 6 or groups of encodedspectral coefficients which belong to a non-tonal background noisebetween signal harmonics of the audio signal 102.

FIG. 5 shows a flowchart of a method 300 for encoding an audio signal,according to an embodiment. The method 300 comprises a step 302 ofdetermining spectral coefficients of the audio signal for a currentframe and at least one previous frame, and a step 304 of selectivelyapplying predictive encoding to a plurality of individual spectralcoefficients or groups of spectral coefficients which are separated byat least one spectral coefficient.

FIG. 6 shows a flowchart of a method 400 for decoding an encoded audiosignal, according to an embodiment. The method 400 comprises a step 402of parsing the encoded audio signal to obtain encoded spectralcoefficients of the audio signal for a current frame and at least oneprevious frame, and a step 404 of selectively applying predictivedecoding to a plurality of individual encoded spectral coefficients orgroups of encoded spectral coefficients which are separated by at leastone encoded spectral coefficient.

Although some aspects have been described in the context of anapparatus, it is clear that these aspects also represent a descriptionof the corresponding method, where a block or device corresponds to amethod step or a feature of a method step. Analogously, aspectsdescribed in the context of a method step also represent a descriptionof a corresponding block or item or feature of a correspondingapparatus. Some or all of the method steps may be executed by (or using)a hardware apparatus, like for example, a microprocessor, a programmablecomputer or an electronic circuit. In some embodiments, one or more ofthe most important method steps may be executed by such an apparatus.

The inventive encoded audio signal can be stored on a digital storagemedium or can be transmitted on a transmission medium such as a wirelesstransmission medium or a wired transmission medium such as the Internet.

Depending on certain implementation requirements, embodiments of theinvention can be implemented in hardware or in software. Theimplementation can be performed using a digital storage medium, forexample a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a PROM, an EPROM,an EEPROM or a FLASH memory, having electronically readable controlsignals stored thereon, which cooperate (or are capable of cooperating)with a programmable computer system such that the respective method isperformed. Therefore, the digital storage medium may be computerreadable.

Some embodiments according to the invention comprise a data carrierhaving electronically readable control signals, which are capable ofcooperating with a programmable computer system, such that one of themethods described herein is performed.

Generally, embodiments of the present invention can be implemented as acomputer program product with a program code, the program code beingoperative for performing one of the methods when the computer programproduct runs on a computer. The program code may for example be storedon a machine readable carrier.

Other embodiments comprise the computer program for performing one ofthe methods described herein, stored on a machine readable carrier.

In other words, an embodiment of the inventive method is, therefore, acomputer program having a program code for performing one of the methodsdescribed herein, when the computer program runs on a computer.

A further embodiment of the inventive methods is, therefore, a datacarrier (or a digital storage medium, or a computer-readable medium)comprising, recorded thereon, the computer program for performing one ofthe methods described herein. The data carrier, the digital storagemedium or the recorded medium are typically tangible and/ornon-transitionary.

A further embodiment of the inventive method is, therefore, a datastream or a sequence of signals representing the computer program forperforming one of the methods described herein. The data stream or thesequence of signals may for example be configured to be transferred viaa data communication connection, for example via the Internet.

A further embodiment comprises a processing means, for example acomputer, or a programmable logic device, configured to or adapted toperform one of the methods described herein.

A further embodiment comprises a computer having installed thereon thecomputer program for performing one of the methods described herein.

A further embodiment according to the invention comprises an apparatusor a system configured to transfer (for example, electronically oroptically) a computer program for performing one of the methodsdescribed herein to a receiver. The receiver may, for example, be acomputer, a mobile device, a memory device or the like. The apparatus orsystem may, for example, comprise a file server for transferring thecomputer program to the receiver.

In some embodiments, a programmable logic device (for example a fieldprogrammable gate array) may be used to perform some or all of thefunctionalities of the methods described herein. In some embodiments, afield programmable gate array may cooperate with a microprocessor inorder to perform one of the methods described herein. Generally, themethods are advantageously performed by any hardware apparatus.

The apparatus described herein may be implemented using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

The methods described herein may be performed using a hardwareapparatus, or using a computer, or using a combination of a hardwareapparatus and a computer.

While this invention has been described in terms of several embodiments,there are alterations, permutations, and equivalents which fall withinthe scope of this invention. It should also be noted that there are manyalternative ways of implementing the methods and compositions of thepresent invention. It is therefore intended that the following appendedclaims be interpreted as including all such alterations, permutationsand equivalents as fall within the true spirit and scope of the presentinvention.

The invention claimed is:
 1. An encoder for encoding an audio signal,wherein the encoder is configured to encode the audio signal in atransform domain or filter-bank domain, wherein the encoder isconfigured to determine spectral coefficients of the audio signal for acurrent frame and at least one previous frame, wherein the encoder isconfigured to selectively apply predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the encoder is configured to determine a spacing value, whereinthe encoder is configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the spacingvalue is a harmonic spacing value describing a spacing betweenharmonics; wherein the encoder is configured to predictively encode theplurality of individual spectral coefficients or the groups of spectralcoefficients of the current frame, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; wherein the encoder is configured to determine theplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients for the current frame usingcorresponding quantized versions of the plurality of individual spectralcoefficients or the groups of spectral coefficients of the previousframe; wherein the encoder is configured to derive predictioncoefficients from the spacing value, and wherein the encoder isconfigured to calculate the plurality of predicted individual spectralcoefficients or groups of predicted spectral coefficients for thecurrent frame using corresponding quantized versions of the plurality ofindividual spectral coefficients or the groups of spectral coefficientsof at least two previous frames and using the derived predictioncoefficients.
 2. The encoder according to claim 1, wherein the pluralityof individual spectral coefficients or groups of spectral coefficientsare separated by at least one spectral coefficient.
 3. The encoderaccording to claim 2, wherein the predictive encoding is not applied tothe at least one spectral coefficient by which the individual spectralcoefficients or the groups of spectral coefficients are separated. 4.The encoder according to claim 1, wherein the encoder is configured toderive prediction coefficients from the spacing value, and wherein theencoder is configured to calculate the plurality of predicted individualspectral coefficients or groups of predicted spectral coefficients forthe current frame using a corresponding plurality of individual spectralcoefficients or corresponding groups of spectral coefficients of atleast two previous frames and using the derived prediction coefficients.5. The encoder according to claim 4, wherein the encoder is configuredto provide an encoded audio signal, the encoded audio signal notcomprising the prediction coefficients or encoded versions thereof. 6.The encoder according to claim 1, wherein the encoder is configured toprovide an encoded audio signal, the encoded audio signal comprisingquantized versions of the prediction errors instead of quantizedversions of the plurality of individual spectral coefficients or of thegroups of spectral coefficients for the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied.
 7. The encoder according to claim 6, wherein theencoded audio signal comprises quantized versions of the spectralcoefficients to which predictive encoding is not applied, such thatthere is an alternation of spectral coefficients or groups of spectralcoefficients for which quantized versions of the prediction errors arecomprised by the encoded audio signal and spectral coefficients orgroups of spectral coefficients for which quantized versions areprovided without using predictive encoding.
 8. The encoder according toclaim 1, wherein the encoder is configured to determine an instantaneousfundamental frequency of the audio signal and to derive the spacingvalue from the instantaneous fundamental frequency or a fraction or amultiple thereof.
 9. The encoder according to claim 1, wherein theencoder is configured to select individual spectral coefficients orgroups of spectral coefficients spectrally arranged according to aharmonic grid defined by the spacing value for a predictive encoding.10. The encoder according to claim 1, wherein the encoder is configuredto select spectral coefficients, spectral indices of which are equal toor lie within a range around a plurality of spectral indices derived onthe basis of the spacing value, for a predictive encoding.
 11. Theencoder according to claim 10, wherein the encoder is configured to seta width of the range in dependence on the spacing value.
 12. The encoderaccording to claim 1, wherein the encoder is configured to select theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied such that there isa periodic alternation, periodic with a tolerance of +/−1 spectralcoefficient, between the plurality of individual spectral coefficientsor groups of spectral coefficients to which predictive encoding isapplied and the spectral coefficients or groups of spectral coefficientsto which predictive encoding is not applied.
 13. The encoder accordingto claim 1, wherein the audio signal comprises at least two harmonicsignal components, wherein the encoder is configured to selectivelyapply predictive encoding to those plurality of individual spectralcoefficients or groups of spectral coefficients which represent the atleast two harmonic signal components or spectral environments around theat least two harmonic signal components of the audio signal.
 14. Theencoder according to claim 13, wherein the encoder is configured to notapply predictive encoding to those plurality of individual spectralcoefficients or groups of spectral coefficients which do not representthe at least two harmonic signal components or spectral environments ofthe at least two harmonic signal components of the audio signal.
 15. Theencoder according to claim 13, wherein the encoder is configured to notapply predictive encoding to those plurality of individual spectralcoefficients or groups of spectral coefficients which belong to anon-tonal background noise between signal harmonics.
 16. The encoderaccording to claim 13, wherein the spacing value is a harmonic spacingvalue indicating a spectral spacing between the at least two harmonicsignal components of the audio signal, the harmonic spacing valueindicating those plurality of individual spectral coefficients or groupsof spectral coefficients which represent the at least two harmonicsignal components of the audio signal.
 17. The encoder according toclaim 1, wherein the encoder is configured to provide an encoded audiosignal, wherein the encoder is configured to comprise in the encodedaudio signal the spacing value or an encoded version thereof.
 18. Theencoder according to claim 1, wherein the spectral coefficients arespectral bins.
 19. A decoder for decoding an encoded audio signal,wherein the decoder is configured to decode the encoded audio signal ina transform domain or filter-bank domain, wherein the decoder isconfigured to parse the encoded audio signal to acquire encoded spectralcoefficients of the audio signal for a current frame and at least oneprevious frame, and wherein the decoder is configured to selectivelyapply predictive decoding to a plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients, wherein thedecoder is configured to acquire a spacing value, wherein the decoder isconfigured to select the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients to whichpredictive decoding is applied based on the spacing value; wherein thespacing value is a harmonic spacing value describing a spacing betweenharmonics; wherein the decoder is configured to decode the encoded audiosignal in order to acquire quantized prediction errors instead of aplurality of individual quantized spectral coefficients or groups ofquantized spectral coefficients for the plurality of individual encodedspectral coefficients or groups of encoded spectral coefficients towhich predictive decoding is applied; wherein the decoder is configuredto decode the encoded audio signal in order to acquire quantizedspectral coefficients for encoded spectral coefficients to whichpredictive decoding is not applied, such that there is an alternation ofencoded spectral coefficients or groups of encoded spectral coefficientsfor which quantized prediction errors are acquired and encoded spectralcoefficients or groups of encoded spectral coefficients for whichquantized spectral coefficients are acquired.
 20. The decoder accordingto claim 19, wherein the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients are separated byat least one encoded spectral coefficient.
 21. The decoder according toclaim 20, wherein the predictive decoding is not applied to the at leastone spectral coefficient by which the individual spectral coefficientsor the group of spectral coefficients are separated.
 22. The decoderaccording to claim 19, wherein the decoder is configured to entropydecode the encoded spectral coefficients, to acquire quantizedprediction errors for the spectral coefficients to which predictivedecoding is to be applied and quantized spectral coefficients forspectral coefficients to which predictive decoding is not to be applied;and wherein the decoder is configured to apply the quantized predictionerrors to a plurality of predicted individual spectral coefficients orgroups of predicted spectral coefficients, to acquire, for the currentframe, decoded spectral coefficients associated with the encodedspectral coefficients to which predictive decoding is applied.
 23. Thedecoder according to claim 22, wherein the decoder is configured todetermine the plurality of predicted individual spectral coefficients orgroups of predicted spectral coefficients for the current frame based ona corresponding plurality of the individual encoded spectralcoefficients or groups of encoded spectral coefficients of the previousframe.
 24. The decoder according to claim 23, wherein the decoder isconfigured to derive prediction coefficients from the spacing value, andwherein the decoder is configured to calculate the plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients for the current frame using a correspondingplurality of previously decoded individual spectral coefficients orgroups of previously decoded spectral coefficients of at least twoprevious frames and using the derived prediction coefficients.
 25. Thedecoder according to claim 19, wherein the decoder is configured toselect individual spectral coefficients or groups of spectralcoefficients spectrally arranged according to a harmonic grid defined bythe spacing value for a predictive decoding.
 26. The decoder accordingto claim 19, wherein the decoder is configured to select spectralcoefficients, spectral indices of which are equal to or lie within arange around a plurality of spectral indices derived on the basis of thespacing value, for a predictive decoding.
 27. The decoder according toclaim 26, wherein the decoder is configured to set a width of the rangein dependence on the spacing value.
 28. The decoder according to claim19, wherein the encoded audio signal comprises the spacing value or anencoded version thereof, wherein the decoder is configured to extractthe spacing value or the encoded version thereof from the encoded audiosignal to acquire the spacing value.
 29. The decoder according to claim19, wherein the decoder is configured to determine the spacing value.30. The decoder according to claim 29, wherein the decoder is configuredto determine an instantaneous fundamental frequency and to derive thespacing value from the instantaneous fundamental frequency or a fractionor a multiple thereof.
 31. The decoder according to claim 19, whereinthe audio signal represented by the encoded audio signal comprises atleast two harmonic signal components, wherein the decoder is configuredto selectively apply predictive decoding to those plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients which represent the at least two harmonic signal componentsor spectral environments around the at least two harmonic signalcomponents of the audio signal.
 32. The decoder according to claim 31,wherein the decoder is configured to identify the at least two harmonicsignal components, and to selectively apply predictive decoding to thoseplurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients which are associated with the identifiedharmonic signal components.
 33. The decoder according to claim 31,wherein the encoded audio signal comprises the spacing value or anencoded version thereof, wherein the spacing value identifies the atleast two harmonic signal components, wherein the decoder is configuredto selectively apply predictive decoding to those plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients which are associated with the identified harmonic signalcomponents.
 34. The decoder according to claim 31, wherein the decoderis configured to not apply predictive decoding to those plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients which do not represent the at least two harmonic signalcomponents or spectral environments of the at least two harmonic signalcomponents of the audio signal.
 35. The decoder according to claim 31,wherein the decoder is configured to not apply predictive decoding tothose plurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients which belong to a non-tonal backgroundnoise between signal harmonics of the audio signal.
 36. The decoderaccording to claim 19, wherein the encoded audio signal comprises thespacing value or an encoded version thereof, wherein the spacing valueis a harmonic spacing value, the harmonic spacing value indicating thoseplurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients which represent at least two harmonicsignal components of the audio signal.
 37. The decoder according toclaim 19, wherein the spectral coefficients are spectral bins.
 38. Anencoder for encoding an audio signal, wherein the encoder is configuredto encode the audio signal in a transform domain or filter-bank domain,wherein the encoder is configured to determine spectral coefficients ofthe audio signal for a current frame and at least one previous frame,wherein the encoder is configured to selectively apply predictiveencoding to a plurality of individual spectral coefficients or groups ofspectral coefficients, wherein the encoder is configured to determine aspacing value, wherein the encoder is configured to select the pluralityof individual spectral coefficients or groups of spectral coefficientsto which predictive encoding is applied based on the spacing value;wherein the encoder is configured to predictively encode the pluralityof individual spectral coefficients or the groups of spectralcoefficients of the current frame, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; wherein the encoder is configured to deriveprediction coefficients from the spacing value, and wherein the encoderis configured to calculate the plurality of predicted individualspectral coefficients or groups of predicted spectral coefficients forthe current frame using a corresponding plurality of individual spectralcoefficients or corresponding groups of spectral coefficients of atleast two previous frames and using the derived prediction coefficients;and wherein the encoder is configured to select spectral coefficients,spectral indices of which are equal to or lie within a range around aplurality of spectral indices derived on the basis of the spacing value,for a predictive encoding.
 39. An encoder for encoding an audio signal,wherein the encoder is configured to encode the audio signal in atransform domain or filter-bank domain, wherein the encoder isconfigured to determine spectral coefficients of the audio signal for acurrent frame and at least one previous frame, wherein the encoder isconfigured to selectively apply predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the encoder is configured to determine a spacing value, whereinthe encoder is configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the encoder isconfigured to predictively encode the plurality of individual spectralcoefficients or the groups of spectral coefficients of the currentframe, by coding prediction errors between a plurality of predictedindividual spectral coefficients or groups of predicted spectralcoefficients of the current frame and the plurality of individualspectral coefficients or groups of spectral coefficients of the currentframe; wherein the encoder is configured to determine the plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients for the current frame using correspondingquantized versions of the plurality of individual spectral coefficientsor the groups of spectral coefficients of the previous frame; whereinthe encoder is configured to derive prediction coefficients from thespacing value, and wherein the encoder is configured to calculate theplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients for the current frame usingcorresponding quantized versions of the plurality of individual spectralcoefficients or the groups of spectral coefficients of at least twoprevious frames and using the derived prediction coefficients; andwherein the encoder is configured to select spectral coefficients,spectral indices of which are equal to or lie within a range around aplurality of spectral indices derived on the basis of the spacing value,for a predictive encoding.
 40. A decoder for decoding an encoded audiosignal, wherein the decoder is configured to decode the encoded audiosignal in a transform domain or filter-bank domain, wherein the decoderis configured to parse the encoded audio signal to acquire encodedspectral coefficients of the audio signal for a current frame and atleast one previous frame, and wherein the decoder is configured toselectively apply predictive decoding to a plurality of individualencoded spectral coefficients or groups of encoded spectralcoefficients, wherein the decoder is configured to acquire a spacingvalue, wherein the decoder is configured to select the plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients to which predictive decoding is applied based on thespacing value; wherein the decoder is configured to entropy decode theencoded spectral coefficients, to acquire quantized prediction errorsfor the spectral coefficients to which predictive decoding is to beapplied and quantized spectral coefficients for spectral coefficients towhich predictive decoding is not to be applied; wherein the decoder isconfigured to apply the quantized prediction errors to a plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients, to acquire, for the current frame, decodedspectral coefficients associated with the encoded spectral coefficientsto which predictive decoding is applied; wherein the decoder isconfigured to determine the plurality of predicted individual spectralcoefficients or groups of predicted spectral coefficients for thecurrent frame based on a corresponding plurality of the individualencoded spectral coefficients or groups of encoded spectral coefficientsof the previous frame; wherein the decoder is configured to deriveprediction coefficients from the spacing value, and wherein the decoderis configured to calculate the plurality of predicted individualspectral coefficients or groups of predicted spectral coefficients forthe current frame using a corresponding plurality of previously decodedindividual spectral coefficients or groups of previously decodedspectral coefficients of at least two previous frames and using thederived prediction coefficients; wherein the decoder is configured toselect spectral coefficients, spectral indices of which are equal to orlie within a range around a plurality of spectral indices derived on thebasis of the spacing value, for a predictive decoding.
 41. A method forencoding an audio signal in a transform domain or filter-bank domain,the method comprising: determining spectral coefficients of the audiosignal for a current frame and at least one previous frame; determininga spacing value; selectively applying predictive encoding to a pluralityof individual spectral coefficients or groups of spectral coefficients,wherein the plurality of individual spectral coefficients or groups ofspectral coefficients to which predictive encoding is applied areselected based on the spacing value; predictively encoding the pluralityof individual spectral coefficients or the groups of spectralcoefficients of the current frame, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; determining the plurality of predicted individualspectral coefficients or groups of predicted spectral coefficients forthe current frame using corresponding quantized versions of theplurality of individual spectral coefficients or the groups of spectralcoefficients of the previous frame; deriving prediction coefficientsfrom the spacing value, and wherein the encoder is configured tocalculate the plurality of predicted individual spectral coefficients orgroups of predicted spectral coefficients for the current frame usingcorresponding quantized versions of the plurality of individual spectralcoefficients or the groups of spectral coefficients of at least twoprevious frames and using the derived prediction coefficients; whereinthe spacing value is a harmonic spacing value describing a spacingbetween harmonics.
 42. A method for encoding an audio signal in atransform domain or filter-bank domain, the method comprising:determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value;selectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value, wherein the plurality of individual spectralcoefficients or the groups of spectral coefficients of the current frameare predictively encoded, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; deriving prediction coefficients from the spacingvalue; calculating the plurality of predicted individual spectralcoefficients or groups of predicted spectral coefficients for thecurrent frame using a corresponding plurality of individual spectralcoefficients or corresponding groups of spectral coefficients of atleast two previous frames and using the derived prediction coefficients;and selecting spectral coefficients, spectral indices of which are equalto or lie within a range around a plurality of spectral indices derivedon the basis of the spacing value, for a predictive encoding.
 43. Amethod for encoding an audio signal in a transform domain or filter-bankdomain, the method comprising: determining spectral coefficients of theaudio signal for a current frame and at least one previous frame;determining a spacing value; selectively applying predictive encoding toa plurality of individual spectral coefficients or groups of spectralcoefficients, wherein the plurality of individual spectral coefficientsor groups of spectral coefficients to which predictive encoding isapplied are selected based on the spacing value; predictively encodingthe plurality of individual spectral coefficients or the groups ofspectral coefficients of the current frame, by coding prediction errorsbetween a plurality of predicted individual spectral coefficients orgroups of predicted spectral coefficients of the current frame and theplurality of individual spectral coefficients or groups of spectralcoefficients of the current frame; determining the plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients for the current frame using correspondingquantized versions of the plurality of individual spectral coefficientsor the groups of spectral coefficients of the previous frame; derivingprediction coefficients from the spacing value; calculating theplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients for the current frame usingcorresponding quantized versions of the plurality of individual spectralcoefficients or the groups of spectral coefficients of at least twoprevious frames and using the derived prediction coefficients; selectingspectral coefficients, spectral indices of which are equal to or liewithin a range around a plurality of spectral indices derived on thebasis of the spacing value, for a predictive encoding.
 44. A method fordecoding an encoded audio signal in a transform domain or filter-bankdomain, the method comprising: parsing the encoded audio signal toacquire encoded spectral coefficients of the audio signal for a currentframe and at least one previous frame; acquiring a spacing value; andselectively applying predictive decoding to a plurality of individualencoded spectral coefficients or groups of encoded spectralcoefficients, wherein the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients to whichpredictive decoding is applied are selected based on the spacing value;decoding the encoded audio signal in order to acquire quantizedprediction errors instead of a plurality of individual quantizedspectral coefficients or groups of quantized spectral coefficients forthe plurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients to which predictive decoding is applied;decoding the encoded audio signal in order to acquire quantized spectralcoefficients for encoded spectral coefficients to which predictivedecoding is not applied, such that there is an alternation of encodedspectral coefficients or groups of encoded spectral coefficients forwhich quantized prediction errors are acquired and encoded spectralcoefficients or groups of encoded spectral coefficients for whichquantized spectral coefficients are acquired; wherein the spacing valueis a harmonic spacing value describing a spacing between harmonics. 45.A method for decoding an encoded audio signal in a transform domain orfilter-bank domain, the method comprising: parsing the encoded audiosignal to acquire encoded spectral coefficients of the audio signal fora current frame and at least one previous frame; acquiring a spacingvalue; and selectively applying predictive decoding to a plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients, wherein the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients to whichpredictive decoding is applied are selected based on the spacing value;entropy decoding the encoded spectral coefficients, to acquire quantizedprediction errors for the spectral coefficients to which predictivedecoding is to be applied and quantized spectral coefficients forspectral coefficients to which predictive decoding is not to be applied;applying the quantized prediction errors to a plurality of predictedindividual spectral coefficients or groups of predicted spectralcoefficients, to acquire, for the current frame, decoded spectralcoefficients associated with the encoded spectral coefficients to whichpredictive decoding is applied; determining the plurality of predictedindividual spectral coefficients or groups of predicted spectralcoefficients for the current frame based on a corresponding plurality ofthe individual encoded spectral coefficients or groups of encodedspectral coefficients of the previous frame; deriving predictioncoefficients from the spacing value; calculating the plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients for the current frame using a correspondingplurality of previously decoded individual spectral coefficients orgroups of previously decoded spectral coefficients of at least twoprevious frames and using the derived prediction coefficients; andselecting spectral coefficients, spectral indices of which are equal toor lie within a range around a plurality of spectral indices derived onthe basis of the spacing value, for a predictive decoding.
 46. Anon-transitory digital storage medium having a computer program storedthereon to perform the method for encoding an audio signal in atransform domain or filter-bank domain, said method comprising:determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value; andselectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value; predictively encoding the plurality of individualspectral coefficients or the groups of spectral coefficients of thecurrent frame, by coding prediction errors between a plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients of the current frame and the plurality ofindividual spectral coefficients or groups of spectral coefficients ofthe current frame; determining the plurality of predicted individualspectral coefficients or groups of predicted spectral coefficients forthe current frame using corresponding quantized versions of theplurality of individual spectral coefficients or the groups of spectralcoefficients of the previous frame; deriving prediction coefficientsfrom the spacing value, and wherein the encoder is configured tocalculate the plurality of predicted individual spectral coefficients orgroups of predicted spectral coefficients for the current frame usingcorresponding quantized versions of the plurality of individual spectralcoefficients or the groups of spectral coefficients of at least twoprevious frames and using the derived prediction coefficients; whereinthe spacing value is a harmonic spacing value describing a spacingbetween harmonics, when said computer program is run by a computer. 47.A non-transitory digital storage medium having a computer program storedthereon to perform the method for encoding an audio signal in atransform domain or filter-bank domain, said method comprising:determining spectral coefficients of the audio signal for a currentframe and at least one previous frame; determining a spacing value;selectively applying predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theplurality of individual spectral coefficients or groups of spectralcoefficients to which predictive encoding is applied are selected basedon the spacing value, wherein the plurality of individual spectralcoefficients or the groups of spectral coefficients of the current frameare predictively encoded, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; deriving prediction coefficients from the spacingvalue; calculating the plurality of predicted individual spectralcoefficients or groups of predicted spectral coefficients for thecurrent frame using a corresponding plurality of individual spectralcoefficients or corresponding groups of spectral coefficients of atleast two previous frames and using the derived prediction coefficients;and selecting spectral coefficients, spectral indices of which are equalto or lie within a range around a plurality of spectral indices derivedon the basis of the spacing value, for a predictive encoding, when saidcomputer program is run by a computer.
 48. A non-transitory digitalstorage medium having a computer program stored thereon to perform themethod for encoding an audio signal in a transform domain or filter-bankdomain, said method comprising: determining spectral coefficients of theaudio signal for a current frame and at least one previous frame;determining a spacing value; selectively applying predictive encoding toa plurality of individual spectral coefficients or groups of spectralcoefficients, wherein the plurality of individual spectral coefficientsor groups of spectral coefficients to which predictive encoding isapplied are selected based on the spacing value; predictively encodingthe plurality of individual spectral coefficients or the groups ofspectral coefficients of the current frame, by coding prediction errorsbetween a plurality of predicted individual spectral coefficients orgroups of predicted spectral coefficients of the current frame and theplurality of individual spectral coefficients or groups of spectralcoefficients of the current frame; determining the plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients for the current frame using correspondingquantized versions of the plurality of individual spectral coefficientsor the groups of spectral coefficients of the previous frame; derivingprediction coefficients from the spacing value; calculating theplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients for the current frame usingcorresponding quantized versions of the plurality of individual spectralcoefficients or the groups of spectral coefficients of at least twoprevious frames and using the derived prediction coefficients; selectingspectral coefficients, spectral indices of which are equal to or liewithin a range around a plurality of spectral indices derived on thebasis of the spacing value, for a predictive encoding, when saidcomputer program is run by a computer.
 49. A non-transitory digitalstorage medium having a computer program stored thereon to perform themethod for decoding an encoded audio signal in a transform domain orfilter-bank domain, said method comprising: parsing the encoded audiosignal to acquire encoded spectral coefficients of the audio signal fora current frame and at least one previous frame; acquiring a spacingvalue; and selectively applying predictive decoding to a plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients, wherein the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients to whichpredictive decoding is applied are selected based on the spacing value;decoding the encoded audio signal in order to acquire quantizedprediction errors instead of a plurality of individual quantizedspectral coefficients or groups of quantized spectral coefficients forthe plurality of individual encoded spectral coefficients or groups ofencoded spectral coefficients to which predictive decoding is applied;decoding the encoded audio signal in order to acquire quantized spectralcoefficients for encoded spectral coefficients to which predictivedecoding is not applied, such that there is an alternation of encodedspectral coefficients or groups of encoded spectral coefficients forwhich quantized prediction errors are acquired and encoded spectralcoefficients or groups of encoded spectral coefficients for whichquantized spectral coefficients are acquired; wherein the spacing valueis a harmonic spacing value describing a spacing between harmonics, whensaid computer program is run by a computer.
 50. A non-transitory digitalstorage medium having a computer program stored thereon to perform themethod for decoding an encoded audio signal in a transform domain orfilter-bank domain, said method comprising: parsing the encoded audiosignal to acquire encoded spectral coefficients of the audio signal fora current frame and at least one previous frame; acquiring a spacingvalue; and selectively applying predictive decoding to a plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients, wherein the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients to whichpredictive decoding is applied are selected based on the spacing value;entropy decoding the encoded spectral coefficients, to acquire quantizedprediction errors for the spectral coefficients to which predictivedecoding is to be applied and quantized spectral coefficients forspectral coefficients to which predictive decoding is not to be applied;applying the quantized prediction errors to a plurality of predictedindividual spectral coefficients or groups of predicted spectralcoefficients, to acquire, for the current frame, decoded spectralcoefficients associated with the encoded spectral coefficients to whichpredictive decoding is applied; determining the plurality of predictedindividual spectral coefficients or groups of predicted spectralcoefficients for the current frame based on a corresponding plurality ofthe individual encoded spectral coefficients or groups of encodedspectral coefficients of the previous frame; deriving predictioncoefficients from the spacing value; calculating the plurality ofpredicted individual spectral coefficients or groups of predictedspectral coefficients for the current frame using a correspondingplurality of previously decoded individual spectral coefficients orgroups of previously decoded spectral coefficients of at least twoprevious frames and using the derived prediction coefficients; andselecting spectral coefficients, spectral indices of which are equal toor lie within a range around a plurality of spectral indices derived onthe basis of the spacing value, for a predictive decoding, when saidcomputer program is run by a computer.
 51. An encoder for encoding anaudio signal, wherein the encoder is configured to encode the audiosignal in a transform domain or filter-bank domain, wherein the encoderis configured to determine spectral coefficients of the audio signal fora current frame and at least one previous frame, wherein the encoder isconfigured to selectively apply predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the encoder is configured to determine a spacing value, whereinthe encoder is configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the spacingvalue is a harmonic spacing value describing a spacing betweenharmonics; wherein the encoder is configured to predictively encode theplurality of individual spectral coefficients or the groups of spectralcoefficients of the current frame, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; wherein the encoder is configured to provide anencoded audio signal, the encoded audio signal comprising quantizedversions of the prediction errors instead of quantized versions of theplurality of individual spectral coefficients or of the groups ofspectral coefficients for the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied, and wherein the encoded audio signal comprisesquantized versions of the spectral coefficients to which predictiveencoding is not applied, such that there is an alternation of spectralcoefficients or groups of spectral coefficients for which quantizedversions of the prediction errors are comprised by the encoded audiosignal and spectral coefficients or groups of spectral coefficients forwhich quantized versions are provided without using predictive encoding.52. An encoder for encoding an audio signal, wherein the encoder isconfigured to encode the audio signal in a transform domain orfilter-bank domain, wherein the encoder is configured to determinespectral coefficients of the audio signal for a current frame and atleast one previous frame, wherein the encoder is configured toselectively apply predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theencoder is configured to determine a spacing value, wherein the encoderis configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the spacingvalue is a harmonic spacing value describing a spacing betweenharmonics; wherein the encoder is configured to select spectralcoefficients, spectral indices of which are equal to or lie within arange around a plurality of spectral indices derived on the basis of thespacing value, for a predictive encoding, and wherein the encoder isconfigured to set a width of the range in dependence on the spacingvalue.
 53. An encoder for encoding an audio signal, wherein the encoderis configured to encode the audio signal in a transform domain orfilter-bank domain, wherein the encoder is configured to determinespectral coefficients of the audio signal for a current frame and atleast one previous frame, wherein the encoder is configured toselectively apply predictive encoding to a plurality of individualspectral coefficients or groups of spectral coefficients, wherein theencoder is configured to determine a spacing value, wherein the encoderis configured to select the plurality of individual spectralcoefficients or groups of spectral coefficients to which predictiveencoding is applied based on the spacing value; wherein the spacingvalue is a harmonic spacing value describing a spacing betweenharmonics; and wherein the encoder is configured to select the pluralityof individual spectral coefficients or groups of spectral coefficientsto which predictive encoding is applied such that there is a periodicalternation, periodic with a tolerance of +/−1 spectral coefficient,between the plurality of individual spectral coefficients or groups ofspectral coefficients to which predictive encoding is applied and thespectral coefficients or groups of spectral coefficients to whichpredictive encoding is not applied.
 54. A decoder for decoding anencoded audio signal, wherein the decoder is configured to decode theencoded audio signal in a transform domain or filter-bank domain,wherein the decoder is configured to parse the encoded audio signal toacquire encoded spectral coefficients of the audio signal for a currentframe and at least one previous frame, and wherein the decoder isconfigured to selectively apply predictive decoding to a plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients, wherein the decoder is configured to acquire a spacingvalue, wherein the decoder is configured to select the plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients to which predictive decoding is applied based on thespacing value; wherein the spacing value is a harmonic spacing valuedescribing a spacing between harmonics; wherein the decoder isconfigured to select spectral coefficients, spectral indices of whichare equal to or lie within a range around a plurality of spectralindices derived on the basis of the spacing value, for a predictivedecoding; and wherein the decoder is configured to set a width of therange in dependence on the spacing value.
 55. A method for encoding anaudio signal in a transform domain or filter-bank domain, the methodcomprising: determining spectral coefficients of the audio signal for acurrent frame and at least one previous frame; determining a spacingvalue; selectively applying predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the plurality of individual spectral coefficients or groups ofspectral coefficients to which predictive encoding is applied areselected based on the spacing value; predictively encoding the pluralityof individual spectral coefficients or the groups of spectralcoefficients of the current frame, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; providing an encoded audio signal, the encodedaudio signal comprising quantized versions of the prediction errorsinstead of quantized versions of the plurality of individual spectralcoefficients or of the groups of spectral coefficients for the pluralityof individual spectral coefficients or groups of spectral coefficientsto which predictive encoding is applied, wherein the encoded audiosignal comprises quantized versions of the spectral coefficients towhich predictive encoding is not applied, such that there is analternation of spectral coefficients or groups of spectral coefficientsfor which quantized versions of the prediction errors are comprised bythe encoded audio signal and spectral coefficients or groups of spectralcoefficients for which quantized versions are provided without usingpredictive encoding; and wherein the spacing value is a harmonic spacingvalue describing a spacing between harmonics.
 56. A method for encodingan audio signal in a transform domain or filter-bank domain, the methodcomprising: determining spectral coefficients of the audio signal for acurrent frame and at least one previous frame; determining a spacingvalue; selectively applying predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the plurality of individual spectral coefficients or groups ofspectral coefficients to which predictive encoding is applied areselected based on the spacing value; selecting spectral coefficients,spectral indices of which are equal to or lie within a range around aplurality of spectral indices derived on the basis of the spacing value,for a predictive encoding, setting a width of the range in dependence onthe spacing value; and wherein the spacing value is a harmonic spacingvalue describing a spacing between harmonics.
 57. A method for encodingan audio signal in a transform domain or filter-bank domain, the methodcomprising: determining spectral coefficients of the audio signal for acurrent frame and at least one previous frame; determining a spacingvalue; selectively applying predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the plurality of individual spectral coefficients or groups ofspectral coefficients to which predictive encoding is applied areselected based on the spacing value; selecting the plurality ofindividual spectral coefficients or groups of spectral coefficients towhich predictive encoding is applied such that there is a periodicalternation, periodic with a tolerance of +/−1 spectral coefficient,between the plurality of individual spectral coefficients or groups ofspectral coefficients to which predictive encoding is applied and thespectral coefficients or groups of spectral coefficients to whichpredictive encoding is not applied; and wherein the spacing value is aharmonic spacing value describing a spacing between harmonics.
 58. Amethod for decoding an encoded audio signal in a transform domain orfilter-bank domain, the method comprising: parsing the encoded audiosignal to acquire encoded spectral coefficients of the audio signal fora current frame and at least one previous frame; acquiring a spacingvalue; and selectively applying predictive decoding to a plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients, wherein the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients to whichpredictive decoding is applied are selected based on the spacing value;selecting spectral coefficients, spectral indices of which are equal toor lie within a range around a plurality of spectral indices derived onthe basis of the spacing value, for a predictive decoding; setting awidth of the range in dependence on the spacing value; and wherein thespacing value is a harmonic spacing value describing a spacing betweenharmonics.
 59. A non-transitory digital storage medium having a computerprogram stored thereon to perform the method for encoding an audiosignal in a transform domain or filter-bank domain, the methodcomprising: determining spectral coefficients of the audio signal for acurrent frame and at least one previous frame; determining a spacingvalue; selectively applying predictive encoding to a plurality ofindividual spectral coefficients or groups of spectral coefficients,wherein the plurality of individual spectral coefficients or groups ofspectral coefficients to which predictive encoding is applied areselected based on the spacing value; predictively encoding the pluralityof individual spectral coefficients or the groups of spectralcoefficients of the current frame, by coding prediction errors between aplurality of predicted individual spectral coefficients or groups ofpredicted spectral coefficients of the current frame and the pluralityof individual spectral coefficients or groups of spectral coefficientsof the current frame; providing an encoded audio signal, the encodedaudio signal comprising quantized versions of the prediction errorsinstead of quantized versions of the plurality of individual spectralcoefficients or of the groups of spectral coefficients for the pluralityof individual spectral coefficients or groups of spectral coefficientsto which predictive encoding is applied, wherein the encoded audiosignal comprises quantized versions of the spectral coefficients towhich predictive encoding is not applied, such that there is analternation of spectral coefficients or groups of spectral coefficientsfor which quantized versions of the prediction errors are comprised bythe encoded audio signal and spectral coefficients or groups of spectralcoefficients for which quantized versions are provided without usingpredictive encoding; wherein the spacing value is a harmonic spacingvalue describing a spacing between harmonics; and when said computerprogram is run by a computer.
 60. A non-transitory digital storagemedium having a computer program stored thereon to perform the methodfor encoding an audio signal in a transform domain or filter-bankdomain, the method comprising: determining spectral coefficients of theaudio signal for a current frame and at least one previous frame;determining a spacing value; selectively applying predictive encoding toa plurality of individual spectral coefficients or groups of spectralcoefficients, wherein the plurality of individual spectral coefficientsor groups of spectral coefficients to which predictive encoding isapplied are selected based on the spacing value; selecting spectralcoefficients, spectral indices of which are equal to or lie within arange around a plurality of spectral indices derived on the basis of thespacing value, for a predictive encoding, setting a width of the rangein dependence on the spacing value; wherein the spacing value is aharmonic spacing value describing a spacing between harmonics; and whensaid computer program is run by a computer.
 61. A non-transitory digitalstorage medium having a computer program stored thereon to perform themethod for encoding an audio signal in a transform domain or filter-bankdomain, the method comprising: determining spectral coefficients of theaudio signal for a current frame and at least one previous frame;determining a spacing value; selectively applying predictive encoding toa plurality of individual spectral coefficients or groups of spectralcoefficients, wherein the plurality of individual spectral coefficientsor groups of spectral coefficients to which predictive encoding isapplied are selected based on the spacing value; selecting the pluralityof individual spectral coefficients or groups of spectral coefficientsto which predictive encoding is applied such that there is a periodicalternation, periodic with a tolerance of +/−1 spectral coefficient,between the plurality of individual spectral coefficients or groups ofspectral coefficients to which predictive encoding is applied and thespectral coefficients or groups of spectral coefficients to whichpredictive encoding is not applied; wherein the spacing value is aharmonic spacing value describing a spacing between harmonics; and whensaid computer program is run by a computer.
 62. A non-transitory digitalstorage medium having a computer program stored thereon to perform themethod for decoding an encoded audio signal in a transform domain orfilter-bank domain, the method comprising: parsing the encoded audiosignal to acquire encoded spectral coefficients of the audio signal fora current frame and at least one previous frame; acquiring a spacingvalue; and selectively applying predictive decoding to a plurality ofindividual encoded spectral coefficients or groups of encoded spectralcoefficients, wherein the plurality of individual encoded spectralcoefficients or groups of encoded spectral coefficients to whichpredictive decoding is applied are selected based on the spacing value;selecting spectral coefficients, spectral indices of which are equal toor lie within a range around a plurality of spectral indices derived onthe basis of the spacing value, for a predictive decoding; setting awidth of the range in dependence on the spacing value; wherein thespacing value is a harmonic spacing value describing a spacing betweenharmonics; and when said computer program is run by a computer.